complete ni-zn battery information

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Pub. No.: WO/2008/036948 International Application No.: PCT/US2007/079237 Publication Date: 27.03.2008 International Filing Date: 21.09.2007 IPC: H02J 7/16 (2006.01), H02J 7/00 (2006.01) Applicants: POWERGENIX SYSTEMS, INC. [US/US]; 10109 Carroll Canyon Road, San Diego, California 92131-1109 (US) (All Except US) . ALGER, Ethan [US/US]; (US) (US Only) . PHILLIPS, Jeffrey [GB/US]; (US) (US Only) . BENDERT, Richard [US/US]; (US) (US Only) . MOHANTA, Samaresh [CA/US]; (US) (US Only) . Inventors: ALGER, Ethan; (US). PHILLIPS, Jeffrey; (US). BENDERT, Richard; (US). MOHANTA, Samaresh; (US). Agent: SHU, Cindy, H. et al. ; Beyer Weaver LLP, P. O. Box 70250, Oakland, California 94612-0250 (US) . Priority Data: 60/846,518 21.09.2006 US Title: CHARGING METHODS FOR NICKEL-ZINC BATTERY PACKS Abstract: A temperature-compensated constant voltage battery charging algorithm charges batteries quickly and safely. Charging algorithms also include methods to recondition batteries after storage and to correct cell imbalances in a battery pack. A battery charger able to perform these functions is also disclosed. Designated States: AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BH, BR, BW, BY, BZ, CA, CH, CN, CO, CR, CU, CZ, DE, DK, DM, DO, DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT, HN, HR, HU, ID, IL, IN, IS, JP, KE, KG, KM, KN, KP, KR, KZ, LA, LC, LK, LR, LS, LT, LU, LY, MA, MD, ME, MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI, NO, NZ, OM, PG, PH, PL, PT, RO, RS, RU, SC, SD, SE, SG, SK, SL, SM, SV, SY, TJ, TM, TN, TR, TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW. African Regional Intellectual Property Org. (ARIPO) (BW, GH, GM, KE, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM, ZW) Eurasian Patent Organization (EAPO) (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM) European Patent Office (EPO) (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GB, GR, HU, IE, IS, IT, LT, LU, LV, MC, MT, NL, PL, PT, RO, SE, SI, SK, TR) African Intellectual Property Organization (OAPI) (BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW, ML, MR, NE, SN, TD, TG). Publication Language: English (EN) Filing Language: English (EN)

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Complete NI-ZN Battery Information

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Page 1: Complete NI-ZN Battery Information

Pub. No.:

WO/2008/036948

International Application No.:

PCT/US2007/079237Publication Date: 27.03.2008 International Filing Date: 21.09.2007

IPC: H02J 7/16 (2006.01), H02J 7/00 (2006.01)

Applicants:

POWERGENIX SYSTEMS, INC. [US/US]; 10109 Carroll Canyon Road, SanDiego, California 92131-1109 (US) (All Except US).ALGER, Ethan [US/US]; (US) (US Only).PHILLIPS, Jeffrey [GB/US]; (US) (US Only).BENDERT, Richard [US/US]; (US) (US Only).MOHANTA, Samaresh [CA/US]; (US) (US Only).

Inventors:

ALGER, Ethan; (US).PHILLIPS, Jeffrey; (US).BENDERT, Richard; (US).MOHANTA, Samaresh; (US).

Agent:SHU, Cindy, H. et al.; Beyer Weaver LLP, P. O. Box 70250, Oakland,California 94612-0250 (US) .

Priority Data: 60/846,518 21.09.2006 US

Title: CHARGING METHODS FOR NICKEL-ZINC BATTERY PACKS

Abstract:

A temperature-compensated constantvoltage battery charging algorithmcharges batteries quickly and safely.Charging algorithms also includemethods to recondition batteries afterstorage and to correct cell imbalances ina battery pack. A battery charger able toperform these functions is alsodisclosed.

DesignatedStates:

AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BH, BR, BW, BY, BZ, CA, CH, CN,CO, CR, CU, CZ, DE, DK, DM, DO, DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH,GM, GT, HN, HR, HU, ID, IL, IN, IS, JP, KE, KG, KM, KN, KP, KR, KZ, LA,LC, LK, LR, LS, LT, LU, LY, MA, MD, ME, MG, MK, MN, MW, MX, MY, MZ, NA,NG, NI, NO, NZ, OM, PG, PH, PL, PT, RO, RS, RU, SC, SD, SE, SG, SK, SL,SM, SV, SY, TJ, TM, TN, TR, TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW.African Regional Intellectual Property Org. (ARIPO) (BW, GH, GM, KE, LS,MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM, ZW)Eurasian Patent Organization (EAPO) (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM)European Patent Office (EPO) (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI,FR, GB, GR, HU, IE, IS, IT, LT, LU, LV, MC, MT, NL, PL, PT, RO, SE, SI, SK,TR)African Intellectual Property Organization (OAPI) (BF, BJ, CF, CG, CI, CM,GA, GN, GQ, GW, ML, MR, NE, SN, TD, TG).

Publication Language: English (EN)

Filing Language: English (EN)

Page 2: Complete NI-ZN Battery Information

PowerGenix Nickel-Zinc Charge ProcedureTwo Step Charge1. Constant Current: From 1.0 to 2.0 Amps to 1.9V/Cell2. Constant Voltage: 1.9V/Cell to Current < 90mAFault Conditions* Total charge time exceeds 2.5 hrs* Temperature of the cell rises by more than 15C* Voltage is less than 1.6VNotes: For Laboratory Testing: Non temperature compensation at 25°C +/_ 3 degreesTemperature Compensated Charge ProcedureTwo Step Charge*Temperature Compensated Voltage (TCV) = 1.90 - (0.003 x (T-25ºC) V/Cell* Constant Current 2A to TCV* Constant Voltage TCV to I < 90 mAFault ConditionsStop Charge if the any of the following conditions occur:* Total charge time exceeds 2.5 hrs* Temperature of the cell rises by more than 15ºC*Temperature of the cell exceeds 40ºC*Voltage is less than 1.6VCharge Characteristics at 25°CMaintenance Charge ProcedureRecharge cell/pack per Standard Charge Procedure if:Volts per cell < 1.68 VTime since last full charge > 30 days

WO 2008036948 20080327CHARGING METHODS FOR NICKEL-ZINC BATTERY PACKSFIELD OF THE INVENTIONThe present invention relates to the rechargeable battery arts and, more particularly to nickelzinc rechargeable battery cells and packs. Even more specifically, this invention pertains tomethods of charging sealed nickel zinc rechargeable battery cells.BACKGROUNDThe method of charging a nickel zinc battery is important to its performance. Performancefactors such as battery life, specific capacity, charging time, and cost can all be affected by themethod of charging. Charger designers must balance the need for a fast charge, therefore aquick return to service, and low cost charger with the other needs such as cell balancing,increasing life, and preserving capacity.Nickel zinc battery charging poses particular challenges because the nickel electrode chargingpotential exists at a voltage very close to the oxygen evolution potential. During batterycharging, the oxygen evolution process competes with the nickel electrode charging process as afunction of the state-of-charge of the nickel electrode, charging current density, geometry, and

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temperature.During the charging of a conventionally designed nickel zinc cell with excess zinc, oxygenevolution occurs before the nickel becomes fully charged. Nickel zinc batteries use membraneseparators between the electrodes that limit the transport and oxygen access to the zincelectrode for direct recombination. Therefore, the rate at which oxygen can recombine at thezinc electrode is limited because the oxygen must travel to the ends of the electrode to crossthe membrane separator. This challenge is particular to the nickel zinc battery because someother battery types, such as nickel cadmium batteries, do not employ separators having thesame resistance to oxygen mobility. Thus, nickel zinc batteries are limited by their relativelylower oxygen recombination rates. In a sealed cell in the oxygen evolution regime, chargingcurrent density must not exceed the threshold above which oxygen would be created faster thanthe recombination within the cell, or oxygen pressure will build up.Because of the oxygen evolution, the nickel zinc battery may require an "overcharge" to fullyreplace the nickel electrode's capacity. In other nickel battery types' charging schemes, thisovercharge can be performed reasonably quickly. In the case for nickel zinc, however, the lowerrecombination rate limits the use of overcharging to cure the imbalance. Instead ofovercharging at the rate of C/3 for nickel cadmium batteries, nickel zinc batteries can onlyovercharge at the rate of between C/100 and C/10, typically between 40 and 200 milliamps for2 Amp-hour cells.Classic charging schemes include constant potential and constant current. In order to avoidoxygen pressure build up in nickel zinc cells, a constant current scheme could necessitate toolow of a current to allow fast charging. In a constant voltage scheme, cell imbalances areexacerbated to reduce the life of battery packs. When the voltage is constant, the weaker cellin series with stronger cells charges at a lower voltage than the stronger cells, furtherexacerbating its lower level of charge. Other charging schemes include multistage constantcurrent schemes and pulse charge with discharge cycles. The more complex is the chargingscheme, the more expensive is the charger.After storage or shipping at high temperature, some battery packs are found to have highimpedance, caused perhaps by a passivation layer on the electrode. These batteries will onlycharge slowly, because the high impedance allows only a low current at constant voltage. At ahigh constant current, these batteries quickly reach the voltage limit. In order to fast chargethese batteries, the passivation layer must be removed to reduce the impedance.What are needed, therefore, are charging methods that are fast, low cost, address chargingimbalances among cells in a battery pack, charge batteries with high impedance, and are safefor the batteries and consumers.SUMMARYThe present invention provides novel charging schemes to quickly charge a nickel zinc batterypack, cure imbalanced cells in a battery pack, cure high impedance resulting during shipment orstorage, and do all this safely and cheaply for the battery and the consumer.Several charging schemes are presented: a bulk charge algorithm for charging most batteries; afront-end charge algorithm for manual and automatic reconditioning of batteries; an end-of-charge termination algorithm; a state-of-charge maintenance charge algorithm to ensure thatthe cell/battery is always charged while attached to a charger; and several alternate chargealgorithms. Any of these may be used alone or in combination. A few preferred combinationsare set forth herein, but the invention is not limited to these.In one aspect, the present invention pertains to a method of charging a nickel- zinc battery at aconstant current, then at a constant voltage. The method includes measuring a temperature ofthe battery, calculating a voltage based on at least the temperature of the battery, charging thebattery at a constant current (CI) until the calculated voltage is reached, charging the batteryat a calculated voltage (CV) per nickel-zinc cell, and stopping the charging at the calculatedvoltage per cell when an end of charge condition is satisfied. Note that there may be one ormore cells in a battery. Typically, the cells are connected in series.During the CI step, the battery is charged at, e.g., 1-2 Amps until either (a) the voltage isequal to or greater than a threshold voltage (which may be temperature compensated)multiplied by the number of cells being charged in series, (b) a specified time has elapsed(e.g., one hour), or (c) the temperature of the battery rises by a specified amount (e.g., about15 degrees Celsius or higher). The battery temperature is optionally measured by athermocouple, thermistor, or other temperature measurement device, typically located in themiddle, or the thermal center, of the battery pack. Note that the parameter values listed hereand elsewhere in this summary were chosen for a typical nickel zinc battery having a capacityof approximately 2 Amp-hours. Those of skill in the art will appreciate that someparameters values may be scaled with the battery capacity. In some embodiments, linearscaling is appropriate.After the optional constant current stage of charging is complete, the bulk charging algorithmproceeds to the CV step. Here the battery is charged at the temperature compensated voltagemultiplied by the number of cells until an end-of charge condition is satisfied. The end-of-charge condition may be that the current reduces to less than or equal to a set value (e.g.,

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about 90 milliamps per cell), a set time has elapsed (e.g., about 1.5 hours), the current isgreater than or equal to a defined threshold value associated with a short circuit in the battery(e.g., about 2.25 Amps for a 2 Amp- hour battery), the temperature rises by a defined amount(e.g., about 15 degrees Celsius or more - e.g., to an temperature of 37 degrees Celsius), or acombination of these.The temperature compensated voltage is a function of the battery temperature and, in someembodiments, a percentage state-of-charge, electrolyte composition, and the constant stagecharge current. Depending on the sophistication of the charging hardware, temperaturecompensation equations of varying complexity may be used. In one embodiment, the chargeremploys a quadratic equation, but other embodiments include a linear equation or two linearequations for different temperature ranges, as shown in Table 1. Equations for various states ofcharge (identified as percentages of complete charge) are provided. Once the temperaturecompensated voltage is determined, it is used in the bulk charge algorithm (e.g., as thevoltage cutoff for the constant current stage of the charge process). The algorithm will updatetemperature compensated voltage as the battery temperature changes over time duringcharging. In certain embodiments, the temperature compensated voltage used during the CVphase is about 1.9 to 1.94 volts. In certain embodiments, this voltage is appropriate for usewhen the cell being charged has a temperature in the range of about 20-25 degrees Celsius,preferably about 22 degrees Celsius. Further, the 1.9 to 1.94 voltage may be appropriate fornickel-zinc batteries having electrolytes with a free unbuffered alkalinity of between about 5and 8.5 molar. In certain embodiments, an expression used for temperature compensatedvoltage during the CV phase is _V=-0.0044*T+2.035 where V is the constant voltage value and T is the temperature in degreesCentigrade.In certain embodiments employing nickel zinc cells employing high conductivity electrolytes,e.g., electrolytes having a conductivity in the range of about 0.5 to 0.6 (ohm cm)"1, theconstant voltage employed during the CV phase may be reduced by some amount. In oneembodiment, the CV set voltage is reduced by about 10 to 20 millivolts compared with thelevel described above. Thus, in some cases, the set voltage during the CV phase may be about1.88 to 1.92 volts. Similarly, the transition from CI to CV may occur when the cell voltagereaches about 1.88 to 1.92 volts during the CI phase in charging a nickel zinc cell.In a particular embodiment, the charging method includes a front-end charge algorithm thatchecks first for battery temperature to be within a certain range, e.g., between about 0 and 45degrees Celsius. If the temperature is outside this range, then the algorithm will apply a tricklecurrent or equivalent current pulse between about 100 to 200 milliamps per 2 amp hour ofbattery capacity until the temperature rises to about 15 degrees Celsius (or other specifiedtemperature), voltage reaches a minimum of, e.g., one volt per cell, or the time limit of, e.g.,about 20hr @ C/20 rate is reached without the temperature increase or minimum voltage. Ifthe temperature is within the range, then the front-end charge algorithm is skipped and theconstant voltage or constant current/constant voltage charging may start.In certain embodiments, a front-end algorithm may be activated automatically by the chargerlogic or manually, e.g., by the user pressing a reconditioning button. If the constant currentstep of the bulk charge algorithm reaches its voltage endpoint (e.g., 1.9 volts) too quickly,e.g., within 0-10 minutes, preferably within 5 minutes, then the front-end algorithm may startautomatically to recondition the battery pack. This algorithm has been found to be helpful forthose batteries having a high impedance resulting from, possibly, passivation during storage orshipping. The lower-than-normal current provided in the front-end charge may reform theelectrode components and thereby remove a passivation layer (e.g., a passivation layer on thezinc electrode).An end-of-charge termination algorithm may be added after the end-of-charge condition issatisfied or may be implemented by a charger when a battery pack has greater than about 90%state-of-charge. In one embodiment, the end-of-charge termination algorithm comprises of afirst corrective current between about 50 to 200milliamps per 2 amp hour of battery capacity for about 30 minutes to 2 hours, preferably atabout 100 milliamps per 2 amp hour of battery capacity for about 1 hour. There is no voltagelimit for this step. This algorithm is found to at least partially overcome cell imbalances in abattery pack. The fixed current forces a certain level of current to pass through each cellequally - thus allowing weaker cells to charge to a level not necessarily attained with constantvoltage and thereby reducing differences between strong and weak cells. The algorithm hasbeen found to increase battery life.The state-of-charge maintenance algorithm can be used to ensure that the cell/battery has,e.g., about 80% or greater state-of-charge while attached to a charger. This algorithm may bea second half of the end-of-charge termination algorithm after the corrective current or maystand alone. One embodiment of this algorithm employs a constant current charge of about0-50 milliamps per 2 amp hour of battery capacity or equivalent current pulsing. In anotherembodiment, the battery pack can receive a full charge cycle (standard charge algorithm)

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periodically if the voltage of the pack is between, e.g., about 1.71V to 1.80V per cell.The temperature compensated voltage used in some of the algorithms may be recalculatedconstantly or periodically. Thus the voltage applied during the constant voltage phase maychange as the battery temperature changes. The temperature measuring and calculatingoperations of the charging method may thus repeat during charging.Certain alternative charge algorithms may include a multi-stepped constant charge algorithm todefined voltage limits (e.g., temperature compensated voltage limits). In some examples,about ten steps are used. In one example, a constant current is applied initially until thevoltage reaches the defined voltage limit. Then the current is stepped down by a defined factoruntil the voltage again reaches the defined limit. The process may repeat until a defined levelof charge is reached. This approach may be employed in cases where very simple chargers areemployed, e.g., chargers that are incapable of performing a constant voltage charge. Thismethod of charging a battery includes measuring a temperature and a voltage of the battery,calculating a calculated voltage based on at least the temperature of the battery, charging thebattery at a charge current until the battery voltage equals the calculated voltage, reducing thecharging current by a defined factor, and charging the battery atthe reduced charge current until the battery voltage equals the calculated voltage. The reducingcurrent and charging the battery at the reduced charge operations may be repeated until thecurrent is below a certain amount, signifying that a certain capacity is reached. The definedfactor may be about 2-10. This factor may be kept constant in some or all of the steps, or maybe varied from step to step. The calculated voltage may be updated continuously by measuringthe temperature and recalculating the voltage. In some embodiments, measuring oftemperature and voltage occurs periodically, e.g., once every 5 seconds. In someembodiments, these measurements occur independently of each other. Certain other alternatecharge algorithms involve using a constant current and terminating the charge based onmeasured voltage, voltage and time, and/or temperature and time. In the first case the chargeis terminated when the voltage level decreases by dV from the maximum, which may be about0 to 0.020 volts/cell in certain embodiments, preferably about 0 volts/cell. In other words, thecharge stops preferably at the inflection point where the voltage stops increasing and is juststarting to decrease from the maximum. In a second case, the charge is terminated when thelevel of voltage decreases relative to time by the amount dV/dt. In other words, the chargerwill terminate the charge when voltage decreases by a pre-determined amount per cell within aspecified time period. Alternatively, the charge may be terminated when the level of voltagedoes not change over a certain amount of time. Lastly, the charge may be terminated based onthe amount of temperature increase relative to time, or dT/dt. In other words, the charger willterminate the charge when the battery temperature increases by a specified amount within aspecified time period.In certain embodiments, a method of charging a nickel-zinc cell may include charging thenickel-zinc battery at a constant current until reaching a point at which (i) the cell's state ofcharge is at least about 70%, (ii) a nickel electrode of the cell has not yet begun to evolveoxygen at a substantial level, and (iii) the cell voltage is between about 1.88 and 1.93 volts orbetween about 1.88 and 1.91 volts; and charging the nickel-zinc battery at a constant voltagein the range of 1.88-1.93 until an end-of- charge condition is satisfied. In some cases, theconstant current may be most about 4 Amps per 2 Amp hour battery capacity when thenickel-zinc battery employs an electrolyte having a conductivity of at least about 0.5 cm"1 ohm~\ In someembodiments, a lower constant current may be used, at about 2 amps or at about 1.5 amps.Note that in this embodiment, no measurement of cell temperature or calculation is necessary.Any one or more of the charging methods described herein may be employed on chargers singlyor in combination. The logic required may be hardwired into the charger by using variouselectronic components, be programmed with a low cost programmable logic circuit (PLC), or becustom designed on a chip (e.g., an ASIC). Also the charger may be integrated into a consumerproduct, such as where the logic is programmed into the power tool or device powered by thebattery. In some of these cases, the logic may be implemented in the electric circuitry directlyintegrated into the consumer product, or be a separate module that may or may not bedetachable.The present invention also pertains to a nickel-zinc battery charger. The charger may include anenclosure for holding the nickel-zinc battery, a thermistor configured to thermally couple to abattery during operation, and a controller configured to execute a set of instructions. Thecharger may also include a recondition button. The enclosure need not completely surround thebattery, e.g., the enclosure may have an open face. The enclosure may also have a door or lidto allow for easy access to the battery. During charging operations, the thermistor may contactan external surface of a cell in the thermal center of a battery pack. The set of instructionsmay include instructions to measure a temperature of the battery, calculate a calculatedvoltage, charge the battery at the calculated voltage, and stop the charge at the calculatedvoltage when an end-of-charge condition is detected. The instructions may also include

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instructions to charge the battery at a constant current, charge the battery at a correctivecurrent, or charge the battery at a minimum current. The instructions may also includeinstructions to charge the battery at an initial current when the recondition button is pressed.Additionally, the charger may include other interface with which the user may interact with thecharger or the charger may communicate with the user, e.g., color lights to indicate completionof charging or that the battery is bad. These and other features and advantages of the inventionwill be described in more detail below with reference to the associated drawings.BRIEF DESCRIPTION OF THE DRAWINGSFigure 1 is a simple schematic of a charger connected to a battery pack in accordance with thepresent invention.Figures 2A and 2B are graphs of charge curves at various battery temperatures of constantcurrent charging at 1 Amp and 2 Amps, respectively.Figure 3 is a graph of charge curves for various electrolyte compositions.Figure 4 is a graph of a constant current/constant voltage charge algorithm over time inaccordance with some embodiments of the present invention.Figure 5 is a graph of a battery charging algorithm over time in accordance with someembodiments of the present invention.Figure 6A is an exploded diagram of a nickel zinc battery cell in accordance with the presentinvention.Figure 6B is a diagrammatic cross-sectional view of an assembled nickel zinc battery cell inaccordance with the present invention.Figure 7 presents a diagram of a cap and vent mechanism according to one embodiment of theinvention.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTSIntroductionIn the following detailed description of the present invention, numerous specific embodimentsare set forth in order to provide a thorough understanding of the invention. However, as will beapparent to those skilled in the art, the present invention may be practiced without thesespecific details or by using alternate elements or processes within the spirit and scope of theinvention. In other instances well-known processes, procedures and components have not beendescribed in detail so as not to unnecessarily obscure aspects of the present invention.Although many charging schemes are presented, it should be understood that not all chargingmethods need to be configured on the same charger. A charger may employ these methodssingly or in combination. Further, a charger may or may not allow user interaction to providemanual selection of a charging algorithm or even selection of a parameter within a particularcharging algorithm. Particularly, a"recondition" button may be provided which the user may select to start the front-end chargealgorithm. For truly low cost chargers, user interaction with the charger may be limited to littleif any manual input, relying instead on the logic of the charger.A battery may include one or more cells. If more than one cell, the cells are electricallyconnected to each other serially. In this disclosure, the terms battery and "battery pack" areused interchangeably. Unless otherwise noted, parameters specified herein pertains to a 2 Amphour cell.Figure 1 shows a simple schematic of a charger 104 connected to a 9-cell battery pack. In thedepicted embodiment, a variable alternating current 102 enters the charger 104, which is wiredto a positive terminal 108 and a negative terminal106. The cells are wired in series. A thermocouple or a thermistor 110 is attached to the centerof the battery pack and provides temperature inputs to the charger 104.Bulk Charge Algorithm with Temperature Compensation (CI/CV) A bulk charge algorithmapplies to many charging situations. It is fast and cost effective. If unmitigated, oxygenevolution is particularly problematic in nickel- zinc battery cells. The bulk charge algorithmgenerally includes at least two stages, a constant current (CI) stage where the majority ofcharging, e.g., up to 80% state-of- charge, takes place and a constant voltage (CV) stagewhere efficient charging takes place while taking into account the oxygen evolution. Theconstant voltage (CV) charging at or below a voltage at which the oxygenevolution/recombination reactions may be sustained in balance without undue increase in cellpressure and/ortemperature. In certain embodiments, the CI stage is performed in a step-wise manner, whicheach succeeding step performed at a lower current.During the CI step, the battery is charged at a constant current (e.g., about 1-2 Amps) untilone of various conditions is satisfied. The desired condition is that the charging reaches adefined voltage (e.g., about 1.9 volts/cell) within a reasonable and expected time frame. Inparticular embodiments, the defined voltages are temperature compensated. This definedvoltage may correspond to a state-of-charge at about 70- 80%, or preferably about 80%. Incertain embodiments, the defined voltages depend on battery temperature, electrolytecomposition (e.g., alkalinity) and the initial constant charge current. After the voltage thresholdcondition is satisfied, then the battery transitions to charging in the CV step.

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The temperature compensated voltage is a function of the battery temperature and apercentage state-of-charge. The complexity of the temperature compensation calculation maybe dictated by the level of sophistication of the charger (and consequently its expense). Itsvalue is defined by using, e.g., a quadratic equation, a linear equation, or two linear equationsfor different temperature ranges (above and below 20 degrees Celsius). Table 1 shows theconstant values for each equation for different percentage state-of-charge between 50 and 90percent. The equations are: Quadratic: a (T)2 + b (T) + c Linear: m (T) + V where T is themeasured temperature and a, b, c, m, and V are constants provided in Table 1. Forsophisticated chargers, the quadratic equation may be desirable, as it may closely approximatethe temperature compensated voltage. However, the linear equations are likely used inimplementation when the charger is limited to simpler logic (which is expected to be thesituation with inexpensive chargers (e.g., about US$5/charger)).An important consideration in choosing the appropriate voltage for the termination of theconstant current phase of the charge is the time required for charging. It is desirable to chargebatteries quickly, so that the battery operated device may return quickly to service. Becausecharge transfer to the battery is typically higher during the CI step than during the CV step, it isdesired that bulk of the charging takes place in the CI step. However, oxygen evolutionbecomes a concern after continued charging in the CI regime. For single cells this value may bechosen at a voltage corresponding to the measured charge voltage at a given current atapproximately 70 - 80% state of charge, depending on factors such as battery temperature andconstant charging current. For multicell batteries the voltage value chosen may correspond to alower state of charge, i.e., 50 to 70% depending on the initial Amp hour capacity distributionspread and how that spread may change overthe cycle life of the battery. The state-of-charge at which the CI step is terminated may belimited to a point at which the onset of oxygen evolution occurs during the constant currentcharge curve taking into account the capacity distribution in a battery pack. Appropriate valuesof the voltage and their temperature dependence are illustrated in Table 1.Figure 2A is a graph of charge curves at various battery temperatures of constant currentcharging at 1 Amp. The graph shows battery voltage versus amp hours charged for 1.8 amphour nickel zinc cells at temperatures of 0 to 40 degrees Centigrade. Curve 202 corresponds tothe charge curve at 0 degrees Centigrade. The voltage increased quickly after very littlecharging and increases from about 1.87 volts to about 2.075 volts at 1.8 amp hours,corresponding to 100% state-of-charge (SOC) for these cells. Curve 204 corresponds to thecharge curve for a battery temperature of 10 degrees Centigrade; curve 206, 20 degrees; curve208, 30 degrees; and, curve 210 at 40 degrees Centigrade. As the battery temperatureincreased, a lower voltages correspond to the same charge capacity. For example, at about 1amp hour, corresponding to 56% SOC for a 1.8 amp hour battery, the battery voltage is about1.845 volts for the 400C battery. As the battery temperature decreases the voltage becamehigher and higher at the same SOC. Note that the curves have an "s" shape or upward trend(increasing slope) after a relatively flat plateau. This upward trend generally occurs at relativelyhigher charged capacities. Though not intended to be bound by this theory, it is believed thatthe onset of the upward trend indicates the beginning of undesirable oxygen evolution rate.Generally, battery pressure does not significantly increase and cause a safety concern until thecharged capacity is over 100%. However, even some oxygen evolution in excess of therecombination rate may affect the longevity of internal parts and render the charging lesseffective because not all electrical energy is converted and stored as electrochemical energy.Thus, the battery voltage is desirably kept below this onset voltage during the entire bulkcharging process by switching to a CV step after the CI step reaches this voltage. Thetemperature compensated voltage may also depend on the electrolyte composition and theconstant charging current. Generally, a lower constant charging current reduces the definedvoltage at which the charging transitions to the CV regime. Figure 2B is a graph of chargecurves at various battery temperatures of constant current charging at 2 Amp. As with theexperiments of Figure 2A, these experiments were conducted with nickel zinc cells having acapacity of 1.8 amp hours. Charging curve 212 corresponds to a battery charged at 0 degreesCentigrade; curve 214, 20 degrees; curve 216, 30 degrees, and, curve 218, 40 degreesCentigrade. Compared to Figure 2A, the voltages are generally higher, about up to 30 millivoltsor even up to 50 millivolts higher. Note that the point where voltage starts to increase ata higher rate occurs at a lower charged capacity. Thus, the SOC at the transition between CIand CV may be lower if the constant current is higher (e.g., 2 amps versus 1 amp). Althoughcharging at a higher current generally means that the charge is quicker, this may not always bethe case. High current CI charging may actually result in a longer total charge time if the CIstage must be terminated at a relatively low SOC due to oxygen evolution considerations. Insuch cases, the charge must transition to the relatively slower CV stage earlier in the overallcharge procedure. A specific example may illustrate the point. At a constant current of 2A, abattery may initiate the CV step at about 60% capacity, which occurs after 40 minutes ofcharging. However, the remaining 40% capacity with the CV step can take over an hour. At

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constant current of IA, a battery may initiate the CV step at about 80% capacity after chargingfor about 1.5 hours. The remaining 20% capacity may take half hour more. The difference intotal charging time between a constant current of IA and 2A may be about half an hour. Anoptimal constant current for the CI step may be between 1 and 2 amps for this 1.8 amp hourcell, or about 1.5 amps. The difference between the temperature compensated voltage ofconstant currents at 2 amp and 1 amp may be up to about 30 millivolts or up to about 50millivolts. The difference between the temperature compensated voltage of constant currents at2 amp and 0.133 amp may be up to about 80 millivolts.Table 1 : Example Temperature Compensation ConstantsIncreased electrolyte conductivity may reduce the defined voltage for transition from the CI tothe CV charge stage. Figure 3 is a graph of charge curves for various electrolyte compositions.The electrolyte may be characterized by its conductivity and alkalinity. The composition of theelectrolytes in Figure 3 are summarized in Table 2. Compositions A and E have the highestalkalinity, followed by compositions B, C, and D. Compositions A-D have similar conductivity,but composition E is lower. The charge curve for composition E is 301; for composition A is303; for B, 305; for C, 307; and, for D is 309. Figure 3 shows that the charge curve 401 forcomposition E reaches the highest voltages earliest during the constant current charging at 2amps. Thus, in some embodiments the voltage during the CV stage may be decreased in cellsemploying electrolytes having relatively higher conductivity. Comparing the charge curves ofcompositions A to E suggests to the inventors that nickel zinc cells having an electrolyteconductivity of about 0.5 to 0.6 (ohm cm)"1 may proceed to a the CV phase at a lower cellvoltage, e.g., about 10-20millivolts lower than would be otherwise appropriate for a nickel zinc cell employing electrolytehaving a lower conductivity, e.g., one in the range of about 0.35 to 0.45 (ohm cm)"1. In somebut not all cases, constant voltage during the CV stage may also be conducted at a lower setvoltage (e.g., in the range of about 1.88 to 1.91 volts). In general, the conductivity of anelectrolyte is a complex function of the electrolyte components. Some components of theelectrolytes in Figure 3 are presented in Table 2. Alkalinity is one, but far from the only, drivingfactor in electrolyte conductivity.Table 2: Electrolyte Compositions Tested in Figure 3In summary the voltage values are dependent upon at least the conductivity of the electrolyte,the charging current, the number of cells in the battery and the battery temperature. In oneembodiment, constant currents for a fast charge are between IA and 2A for a 2 Ah battery.In operation, the temperature compensated voltage may be continuously calculated from theupdated temperature measurement of the battery pack. One preferred way to measuretemperature is from a thermocouple or thermistor located in the thermal center of the batterypack, but other methods may be used. Depending on charger design, temperaturemeasurement may be taken intermittently, as in once every minute or a few seconds, orcontinuously if the logic circuit would permit. To manage the oxygen evolution during batterycharging operations at constant voltage, temperature-compensated voltage for about 70-80%state-of-charge may be used.Figure 4 is graph of a constant current/constant voltage charge algorithm over time inaccordance with one embodiment of the present invention. Current is shown on the left y-axis;voltage is shown on the right y-axis. Curve 402 shows the current through the battery pack (6cells, each having a capacity of approximately 2 Amp-hours) over time. At time 0, the current starts at 2 amps and stays constant until voltage 404reaches about 1.9 volts, at about 2200 seconds for the cell tested. The initial voltage gain isvery steep, and then the rate of voltage gain starts to decrease at about 200 seconds. Thevoltage increases almost constantly in this regime, and is then followed by another rateincrease. This period, from about 200 second to 2100 seconds (in the graph), is the regime ofmost efficient charging. The charging battery pack gains most of its stored capacity during thisperiod. As the curve slope increases again, it reaches a shoulder right around the temperaturecompensated voltage. This shoulder signals the beginning of oxygen evolution. The secondcondition that may signal the end of the constant current step is a defined elapsed time (e.g.,the constant current phase ends after one hour has elapsed). It is anticipated that most batterypacks will reach the temperature compensated voltage within one hour. If after one hour thevoltage is still less than the temperature compensated voltage, one of various problems mayhave occurred: the battery may have developed an internal short circuit, the chargermeasurements may be faulty, or some other battery internal problems may have developed. Inthat case the algorithm will not go to the CV step. User intervention may be required.A third condition that may signal the end of the constant current step is if the batterytemperature rises by at least a particular defined amount - e.g., about 15 degrees Celsius ormore. Just like the second condition, the excessive temperature rise signals something may bewrong with the battery pack. Even though nickel zinc batteries are less prone to thermalrunaways that may plague other battery types, excessive thermal energy may mean thatoxygen pressure is building up or higher than normal rates of recombination is occurring. It may

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also mean that the cell has developed a short. When excessive temperature rise has beendetected, the charging algorithm will stop the charging until the user intervenes. The charge canbe restarted once the temperature is within acceptable bounds. If the problem repeats then thebattery should be disposed of.The second step in the CI7CV bulk charge algorithm is the constant voltage step. During thisstep, the battery continues charging at the defined voltage (e.g., a temperature compensatedvoltage) until one of several conditions is satisfied. The first condition is where the currentreduces to below a defined level (e.g., 90 milliamps for a 2 Amp-hour cell). This low currentsignals that the charging is complete because very little electrical energy is now beingconverted into chemical energy. The charge is stopped at this point because the battery isalmost fully charged, denoted as state of charge (SOC) at 100%. In other embodiments,different current levels may be used as the stop point in order to target different percentages ofSOC. After this condition is satisfied, the charging algorithm would end normally.As seen in Figure 2, the battery cell is held at around 1.9 volts during this step, from about2200 to 5000 seconds, as shown on curve 204. The current 202 drops steadily initially and levelsout slowly. As noted above, during this step oxygen evolution would start. The rate of chargehas to be at such a level that oxygen pressure does not build up significantly.The second condition that may signal the end of the constant voltage step is when 1.5 hourshas elapsed. It is anticipated that battery packs employing 2 Amp- hour cells will reach 90milliamps within about 1.5 hours. However, if after 1.5 hours the current is still higher than 90milliamps, the charge is terminated normally. This is not a safety limit just an alternate limit.Just as in the CI step, various safeguard conditions may be built in to ensure the battery is notovercharged or defective. A third condition that may signal the end of the constant voltage stepis if the battery temperature rises by a defined amount such as 15 degrees Celsius or morerelative to a start time. The start time may be the beginning of battery charging or thebeginning of any of the algorithmic steps.Possible problems are the same as the discussion in the CI step. The last condition is if thecurrent increased to an unexpectedly high value of, e.g., 2.25 amps or more. This high currentmight signal an internal short circuit.Understand that many of the specific parameter values recited here (e.g., maximum current,time cutoffs, and temperature compensated voltage constants) are for nickel zinc cells of aparticular capacity. Specifically, the recited values are directed to nickel zinc cells havingapproximately a 2 Amp-hour capacity configured in series in a 6-cell battery pack. Some of thevalues will have be scaled for cells and battery packs of different capacities, as will beunderstood by those of skill in the art.Front-End Charge AlgorithmVarious "front-end" charge algorithms may be employed prior to bulk charging. One class ofsuch algorithms provides diagnostic tests designed to make sure that the battery can besuccessfully charged using the standard charge algorithm. The front-end algorithm may beimplemented before every charge, automatically, or by user initiation.In one embodiment, a front-end charge algorithm checks first for battery temperature within anacceptable range for bulk charging (e.g., between about 0 and 45 degrees Celsius). Bulkcharging will not be initiated if the temperature is outside this range. In such cases, thealgorithm will apply a "trickle" current or equivalent current pulse between about 50 to 200milliamps per 2 Amp-hour capacity until the temperature rises to an acceptable level for bulkcharging (e.g., about 15 degrees Celsius), and/or the cell voltage reaches a minimum of 1 voltper cell, and/or aspecified time limit is reached (e.g., about 20 hours have elapsed). When the minimum voltageand/or the temperature is reached, the bulk charge algorithm may start.In certain embodiments, this algorithm has the voltage and temperature conditions in thedisjunctive. For example, it will be satisfied if either the battery is at least 15 degrees Celsiusor even the voltage is at least lvolt. Under normal operating conditions, both of these will besatisfied. The algorithm is likely used only when the battery is initially charged, after long-termstorage, or the battery is suspected of being damaged. If neither condition is satisfied beforethe time limit occurs, the standard charge algorithm should not begin. If the voltage is belowthe limit the battery needs to be replaced. If the battery is below the temperature limit, thecharge may be reset.This algorithm may also be triggered when the voltage reaches the temperature compensatedvoltage cut off of the CI step in the standard charge algorithm too fast. A 2 Amp-hour batterycharged at 2 Amps would normally reach its temperature compensated voltage in between 30 to60 minutes, but if a passivation layer causes high impedance in the battery, then the time maybe reduced to between 0 and 20 minutes. Alternatively, this front-end algorithm may beactivated by the user pressing a button to recondition the battery (or otherwise manuallyinitiating). This algorithm has been found to be helpful for those batteries having a passivationbuildup. The lower-than-normal current reforms the electrochemical components and therebyremoves the passivation layer.End-of-Charge Termination Algorithm

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An end-of-charge termination algorithm may be added to the end of the standard chargealgorithm. In one embodiment, the end-of-charge termination algorithm comprises applying acorrective current between about 50 to 200 milliamps for about 30 minutes to 2 hours,preferably at about 100 milliamps for about 1 hour (again assuming a nominally 2 Amp-hourcell). These currents may be scaled for cells having a different capacity. This additionaloperation is initiated after the constant voltage portion of the charging algorithm is completed.In a typical application, there is no voltage limit for this step.In another embodiment, the end-of-charge termination algorithm comprises more than oneconstant current step. The first step may apply a constant current between about 50 to 200milliamps for about 30 minutes to 2 hours, preferably at about 100 milliamps for about 1 hour;and the second step would comprise of constant current between about 0 and 50 milliamps foras long as the battery remains on the charger.Figure 5 shows the addition of an end-of-charge algorithm to the bulk charging algorithm. Afterthe constant voltage CV step, current is held constant in the last CI regime, in the graph after5000 seconds. Current 502 is held constant at about 100 milliamps, and voltage 504 slowlyincreases to a little over 2 volts. This algorithm is found to at least partially overcome cellimbalances in a battery pack. The fixed current forces a certain level of current to pass througheach cell equally - thus allowing weaker cells to charge to a level not necessarily attained withconstant voltage and thereby reducing differences between strong and weak cells. The algorithmis found to increase battery life.State-of- Charge Maintenance AlgorithmThe state-of-charge maintenance algorithm can be used to ensure that the cell/battery has,e.g., 80% or greater state-of-charge while attached to a charger. This way, a user caninadvertently leave the charger plugged in for days, weeks, or months and when she retrieves abattery from the charger it will be nearly fully charged and ready for use. One embodiment ofthis algorithm is to use a constant current charge of between about 0 to 50 milliamps orequivalent current pulsing. This constant current charge would be applied without a voltage limitfor as long as the battery remains in the charger. In another embodiment, the battery pack canreceive a full charge cycle (bulk charge algorithm) periodically if the voltage of the pack falls toa particular level; e.g., between about 1.71 and 1.80 volts per cell.Alternate Charge Algorithms Certain alternative charge algorithms may include a multi-steppedconstant charge algorithm to defined voltage limits (e.g., temperature compensated voltagelimits or temperature and current compensated voltage limits). In some examples, about tensteps are used. First a constant current is applied until the voltage reaches the defined voltagelimit. Then the current is stepped down and held constant until the voltage again reaches thedefined limit. The process may repeat until a defined level of charge is reached. This approachmay be employed in cases where very simple chargers are employed, e.g., chargers that areincapable of performing a constant voltage charge. In one embodiment, each time the currentis stepped down, it is stepped by a factor of about 10. Other alternate charge algorithmsinvolve charging at a constant current and then terminating the charge based on measuredvoltage, voltage and time, and/or temperature and time. In the first case the charge isterminated when the level of voltage decreases by dV from the maximum, which may be about0 to 0.020 volts/cellin certain embodiments, preferably about 0 volts/cell. In the second case, the charge isterminated when the level of voltage decreases relative to time by the amount dV/dt. In otherwords, the charger will terminate the charge when voltage decreases by a pre-determinedamount per cell within a specified time period. Alternatively, the charge may be terminatedwhen the level of voltage does not change over a certain amount of time. Lastly, the chargemay be terminated based on the amount of temperature increase relative to time, or dT/dt. Inother words, the charger will terminate the charge when the battery temperature increases by aspecified amount within a specified time period.The Battery ChargerA battery charger may use these algorithms singly or in combination. The logic required may behardwired into the charger by using various electronic components, be programmed with a lowcost programmable logic circuit (PLC), or be custom designed on a chip (e.g., an ASIC). Oneskilled in the art would be able to select the most economical way to deploy the required logic.The charger may be directly integrated into the consumer product, as the logic may beprogrammed into the power tool or device powered by the battery. In some of those cases, thelogic may be implemented in the electric circuitry within the consumer product, or be aseparate module that may or may not be detachable.The nickel-zinc charger may include an enclosure for holding the nickel-zinc battery, athermistor configured to thermally couple to a battery during operation, and a controllerconfigured to execute a set of instructions. The charger may also include a recondition buttonand/or other interface. The enclosure need not completely surround the battery, e.g., theenclosure may have an open face. The enclosure may also have a door or lid to allow for easyaccess to the battery and otherwise keep out dust. Depending on the size and shape of thebattery, many designs exist for the enclosure of a stand alone battery charger.

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During charging operations, the thermistor may contact an external surface of a cell in thethermal center of a battery pack. The thermistor may be rigidly or flexibly attached to theenclosure. In some cases, the thermistor may be inserted manually or automatically after thebattery has correctly seated in the enclosure.The set of instructions may include instructions to measure a temperature of the battery,calculate a calculated voltage, charge the battery at the calculated voltage, and stop the chargeat the calculated voltage when an end-of-charge condition is detected. The instructions mayalso include instructions to charge the battery at a constant current, charge the battery at acorrective current, or charge the battery at aminimum current. The instructions may also include instructions to charge the battery at aninitial current when the recondition button is pressed. Additionally, the charger may includeother interface with which the user may interact with the charger or the charger maycommunicate with the user, e.g., color lights to indicate completion of charging or that thebattery is bad.General Cell StructureFigures 6A and 6B are graphical representations of the main components of a cylindrical powercell according to an embodiment of the invention, with Figure 6A showing an exploded view ofthe cell. Alternating electrode and electrolyte layers are provided in a cylindrical assembly 601(also called a "jellyroll"). The cylindrical assembly or jellyroll 601 is positioned inside a can 613or other containment vessel. A negative collector disk 603 and a positive collector disk 605 areattached to opposite ends of cylindrical assembly 601. The negative and positive collector disksfunction as internal terminals, with the negative collector disk electrically connected to thenegative electrode and the positive collector disk electrically connected to the positiveelectrode. A cap 609 and the can 613 serve as external terminals. In the depicted embodiment,negative collector disk 603 includes a tab 607 for connecting the negative collector disk 603 tocap 609. Positive collector disk 605 is welded or otherwise electrically connected to can 613. Inother embodiments, the negative collector disk connects to the can and the positive collectordisk connects to the cap.The negative and positive collector disks 603 and 605 are shown with perforations, which maybe employed to facilitate bonding to the jellyroll and/or passage of electrolyte from one portionof a cell to another. In other embodiments, the disks may employ slots (radial or peripheral),grooves, or other structures to facilitate bonding and/or electrolyte distribution.A flexible gasket 611 rests on a circumferential bead 615 provided along the perimeter in theupper portion of can 613, proximate to the cap 609. The gasket 611 serves to electricallyisolate cap 609 from can 613. In certain embodiments, the bead 615 on which gasket 611 restsis coated with a polymer coating. The gasket may be any material that electrically isolates thecap from the can. Preferably the material does not appreciably distort at high temperatures;one such material is nylon. In other embodiments, it may be desirable to use a relativelyhydrophobic material to reduce the driving force that causes the alkaline electrolyte to creepand ultimately leak from the cell at seams or other available egress points. An example of aless wettable material is polypropylene.After the can or other containment vessel is filled with electrolyte, the vessel is sealed toisolate the electrodes and electrolyte from the environment as shown in Figure 6B. The gasketis typically sealed by a crimping process. In certain embodiments, a sealing agent is used toprevent leakage. Examples of suitable sealing agents include bituminous sealing agents, tar andVERSAMID® available from Cognis of Cincinnati, OH.In certain embodiments, the cell is configured to operate in an electrolyte "starved" condition.Further, in certain embodiments, the nickel-zinc cells of this invention employ a starvedelectrolyte format. Such cells have relatively low quantities electrolyte in relation to theamount of active electrode material. They can be easily distinguished from flooded cells, whichhave free liquid electrolyte in interior regions of the cell. As discussed in US Patent ApplicationNo. 11/116,113, filed April 26, 2005, titled "Nickel Zinc Battery Design," hereby incorporated byreference, it may be desirable to operate a cell at starved conditions for a variety of reasons. Astarved cell is generally understood to be one in which the total void volume within the cellelectrode stack is not fully occupied by electrolyte. In a typical example, the void volume of astarved cell after electrolyte fill may be at least about 10% of the total void volume before fill.The battery cells of this invention can have any of a number of different shapes and sizes. Forexample, cylindrical cells of this invention may have the diameter and length of conventionalAAA cells, AA cells, A cells, C cells, etc.Custom cell designs are appropriate in some applications. In a specific embodiment, the cellsize is a sub-C cell size of diameter 22 mm and length 43 mm. Note that the present inventionalso may be employed in relatively small prismatic cell formats, as well as various largerformat cells employed for various non-portable applications.Often the profile of a battery pack for, e.g., a power tool or lawn tool will dictate the size andshape of the battery cells. This invention also pertains to battery packs including one or morenickel zinc battery cells of this invention and appropriate casing, contacts, and conductive linesto permit charge and discharge in an electric device.

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Note that the embodiment shown in Figures 6A and 6B has a polarity reverse of that in aconventional NiCd cell, in that the cap is negative and the can is positive. In conventional powercells, the polarity of the cell is such that the cap is positive and the can or vessel is negative.That is, the positive electrode of the cell assembly is electrically connected with the cap and thenegative electrode of the cell assembly is electrically connected with the can that retains thecell assembly. In a certainembodiments of this invention, including that depicted in Figures 6 A and 6B, the polarity of thecell is opposite of that of a conventional cell. Thus, the negative electrode is electricallyconnected with the cap and the positive electrode is electrically connected to the can. It shouldbe understood that in certain embodiments of this invention, the polarity remains the same asin conventional designs - with a positive cap.The can is the vessel serving as the outer housing or casing of the final cell. In conventionalnickel-cadmium cells, where the can is the negative terminal, it is typically nickel-plated steel.As indicated, in this invention the can may be either the negative or positive terminal. Inembodiments in which the can is negative, the can material may be of a composition similar tothat employed in a conventional nickel cadmium battery, such as steel, as long as the materialis coated with another material compatible with the potential of the zinc electrode. Forexample, a negative can may be coated with a material such as copper to prevent corrosion. Inembodiments where the can is positive and the cap negative, the can may be a compositionsimilar to that used in convention nickel-cadmium cells, typically nickel-plated steel.In some embodiments, the interior of the can may be coated with a material to aid hydrogenrecombination. Any material that catalyzes hydrogen recombination may be used. An exampleof such a material is silver oxide. Venting CapAlthough the cell is generally sealed from the environment, the cell may be permitted to ventgases from the battery that are generated during charge and discharge. A typical nickelcadmium cell vents gas at pressures of approximately 200 Pounds per Square Inch (PSI). Insome embodiments, a nickel zinc cell of this invention is designed to operate at this pressureand even higher (e.g., up to about 300 PSI) without the need to vent. This may encouragerecombination of any oxygen and hydrogen generated within the cell. In certain embodiments,the cell is constructed to maintain an internal pressure of up to about 450 PSI and or even up toabout 600 PSI. In other embodiments, a nickel zinc cell is designed to vent gas at relativelylower pressures. This may be appropriate when the design encourages controlled release ofhydrogen and/or oxygen gases without their recombination within the cell.Figure 7 is a representation of a cap 701 and vent mechanism according to one embodiment ofthe invention. The vent mechanism is preferably designed to allow gas but not electrolyte toescape. Cap 701 includes a disk 708 that rests on the gasket,a vent 703 and an upper portion 705 of cap 701. Disk 708 includes a hole 707 that permits gasto escape. Vent 703 covers hole 707 and is displaced by escaping gas. Vent 703 is typicallyrubber, though it may be made of any material that permits gas to escape and withstands hightemperatures. A square vent has been found to work well. Upper portion 705 is welded to disk708 at weld spots 709 and includes holes 711 to allow the gas to escape. The locations of weldspots 709 and 711 shown are purely illustrative and these may be at any suitable location. In apreferred embodiment, the vent mechanism includes a vent cover 713 made of a hydrophobicgas permeable membrane. Examples of vent cover materials include microporouspolypropylene, microporous polyethylene, microporous PTFE, microporous FEP, microporousfluoropolymers, and mixtures and co-polymers thereof (see e.g., US Patent No. 6,949,310 (J.Phillips), "Leak Proof Pressure Relief Valve for Secondary Batteries," issued September 27,2005, which is incorporated herein by reference for all purposes). The material should be ableto withstand high temperatures. In certain embodiments, hydrophobic gas permeablemembranes are used in conjunction with a tortuous gas escape route. Other battery ventingmechanisms are known in the art and are suitable for use with this invention. In certainembodiments, a cell's materials of construction are chosen to provide regions of hydrogenegress. For example, the cells cap or gasket may be made from a hydrogen permeablepolymeric material. In one specific example, the outer annular region of the cell's cap is madefrom a hydrogen permeable material such as an acrylic plastic or one or more of the polymerslisted above. In such embodiments, only the actual terminal (provided in the center of the capand surrounded by the hydrogen permeable material) need be electrically conductive. TheNegative ElectrodeGenerally the negative electrode includes one or more electroactive sources of zinc or zincateions optionally in combination with one or more additional materials such as conductivityenhancing materials, corrosion inhibitors, wetting agents, etc. as described below. When theelectrode is fabricated it will be characterized by certain physical, chemical, and morphologicalfeatures such as coulombic capacity, chemical composition of the active zinc, porosity,tortuosity, etc.In certain embodiments, the electrochemically active zinc source may comprise one or more ofthe following components: zinc oxide, calcium zincate, zinc metal, and various zinc alloys. Anyof these materials may be provided during fabrication and/or be created during normal cell

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cycling. As a particular example,consider calcium zincate, which may be produced from a paste or slurry containing, e.g.,calcium oxide and zinc oxide.If a zinc alloy is employed, it may in certain embodiments include bismuth and/or indium. Incertain embodiments, it may include up to about 20 parts per million lead. A commerciallyavailable source of zinc alloy meeting this composition requirement is PGlOl provided byNoranda Corporation of Canada.The zinc active material may exist in the form of a powder, a granular composition, etc.Preferably, each of the components employed in a zinc electrode paste formulation has arelatively small particle size. This is to reduce the likelihood that a particle may penetrate orotherwise damage the separator between the positive and negative electrodes.Considering electrochemically active zinc components in particular (and other particulateelectrode components as well), such components preferably have a particle size that is nogreater than about 40 or 50 micrometers. In certain embodiments, the material may becharacterized as having no more than about 1% of its particles with a principal dimension (e.g.,diameter or major axis) of greater than about 50 micrometers. Such compositions can beproduced by, for example, sieving or otherwise treating the zinc particles to remove largerparticles. Note that the particle size regimes recited here apply to zinc oxides and zinc alloys aswell as zinc metal powders.In addition to the electrochemically active zinc component(s), the negative electrode mayinclude one or more additional materials that facilitate or otherwise impact certain processeswithin the electrode such as ion transport, electron transport (e.g., enhance conductivity),wetting, porosity, structural integrity (e.g., binding), gassing, active material solubility, barrierproperties (e.g., reducing the amount of zinc leaving the electrode), corrosion inhibition etc.For example, in some embodiments, the negative electrode includes an oxide such as bismuthoxide, indium oxide, and/or aluminum oxide. Bismuth oxide and indium oxide may interactwith zinc and reduce gassing at the electrode. Bismuth oxide may be provided in aconcentration of between about 1 and 10% by weight of a dry negative electrode formulation.It may facilitate recombination of hydrogen and oxygen. Indium oxide may be present in aconcentration of between about 0.05 and 1% by weight of a dry negative electrode formulation.Aluminum oxide may be provided in a concentration of between about 1 and 5% by weight of adry negativeelectrode formulation.In certain embodiments, one or more additives may be included to improve corrosion resistanceof the zinc electroactive material and thereby facilitate long shelf life. The shelf life can becritical to the commercial success or failure of a battery cell. Recognizing that batteries areintrinsically chemically unstable devices, steps should be taken to preserve battery components,including the negative electrode, in their chemically useful form. When electrode materialscorrode or otherwise degrade to a significant extent over weeks or months without use, theirvalue becomes limited by short shelf life. Specific examples of anions that may be included toreduce the solubility of zinc in the electrolyte include phosphate, fluoride, borate, zincate,silicate, stearate, etc. Generally, these anions may be present in a negative electrode inconcentrations of up to about 5% by weight of a dry negative electrode formulation. It isbelieved that at least certain of these anions go into solution during cell cycling and there theyreduce the solubility of zinc. Examples of electrode formulations including these materials areincluded in the following patents and patent applications, each of which is incorporated hereinby reference for all purposes: U.S. Patent No. 6,797,433, issued September 28, 2004, titled,"Negative Electrode Formulation for a Low Toxicity Zinc Electrode Having Additives with RedoxPotentials Negative to Zinc Potential," by Jeffrey Phillips; U.S. Patent No. 6,835,499, issuedDecember 28, 2004, titled, "Negative Electrode Formulation for a Low Toxicity Zinc ElectrodeHaving Additives with Redox Potentials Positive to Zinc Potential," by Jeffrey Phillips; U.S.Patent No. 6,818,350, issued November 16, 2004, titled, "Alkaline Cells Having Low ToxicityRechargeable Zinc Electrodes," by Jeffrey Phillips; and PCT/NZ02/00036 (publication no. WO02/075830) filed March 15, 2002 by Hall et al.Examples of materials that may be added to the negative electrode to improve wetting includetitanium oxides, alumina, silica, alumina and silica together, etc. Generally, these materials areprovided in concentrations of up to about 10% by weight of a dry negative electrodeformulation. A further discussion of such materials may be found in U.S. Patent No. 6,811,926,issued November 2, 2004, titled, "Formulation of Zinc Negative Electrode for Rechargeable CellsHaving an Alkaline Electrolyte," by Jeffrey Phillips, which is incorporated herein by reference forall purposes.Examples of materials that may be added to the negative electrode to improve electronicconductance include various electrode compatible materials having highintrinsic electronic conductivity. Examples include titanium oxides, etc. Generally, thesematerials are provided in concentrations of up to about 10% by weight of a dry negativeelectrode formulation. The exact concentration will depend, of course, on the properties ofchosen additive. Various organic materials may be added to the negative electrode for the

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purpose of binding, dispersion, and/or as surrogates for separators. Examples includehydroxylethyl cellulose (HEC), carboxymethyl cellulose (CMC), the free acid form ofcarboxymethyl cellulose (HCMC), polytetrafluoroethylene (PTFE), polystyrene sulfonate (PSS),polyvinyl alcohol (PVA), nopcosperse dispersants (available from San Nopco Ltd. of KyotoJapan), etc.In a specific example, PSS and PVA are used to coat the negative electrode to provide wettingor other separator-like properties. In certain embodiments, when using a separator-like coatingfor the electrode, the zinc-nickel cell may employ a single layer separator and in someembodiments, no independent separator at all. In certain embodiments, polymeric materialssuch as PSS and PVA may be mixed with the paste formation (as opposed to coating) for thepurpose of burying sharp or large particles in the electrode that might otherwise pose a dangerto the separator.When defining an electrode composition herein, it is generally understood as being applicable tothe composition as produced at the time of fabrication (e.g., the composition of a paste, slurry,or dry fabrication formulation), as well as compositions that might result during or afterformation cycling or during or after one or more charge-discharge cycles while the cell is in usesuch as while powering a portable tool. Various negative electrode compositions within thescope of this invention are described in the following documents, each of which is incorporatedherein by reference: PCT Publication No. WO 02/39517 (J. Phillips), PCT Publication No. WO02/039520 (J. Phillips), PCT Publication No. WO 02/39521, PCT Publication No. WO 02/039534and (J. Phillips), US Patent Publication No. 2002182501. Negative electrode additives in theabove references include, for example, silica and fluorides of various alkaline earth metals,transition metals, heavy metals, and noble metals.Finally, it should be noted that while a number of materials may be added to the negativeelectrode to impart particular properties, some of those materials or properties may beintroduced via battery components other than the negativeelectrode. For example, certain materials for reducing the solubility of zinc in the electrolytemay be provided in the electrolyte or separator (with or without also being provided to thenegative electrode). Examples of such materials include phosphate, fluoride, borate, zincate,silicate, stearate. Other electrode additives identified above that might be provided in theelectrolyte and/or separator include surfactants, ions of indium, bismuth, lead, tin, calcium,etc.US Patent Application No. 10/921,062 (J. Phillips), filed August 17, 2004, hereby incorporatedby reference, describes a method of manufacturing a zinc negative electrode of the type thatmay be employed in the present invention.Negative Electronic Conduction PathwayThe negative electronic pathway is comprised of the battery components that carry electronsbetween the negative electrode and the negative terminal during charge and discharge. One ofthese components is a carrier or current collection substrate on which the negative electrode isformed and supported. This is a subject of the present invention. In a cylindrical cell design, thesubstrate is typically provided within a spirally wound sandwich structure that includes thenegative electrode material, a cell separator and the positive electrode components (includingthe electrode itself and a positive current collection substrate). As indicated, this structure isoften referred to as a jellyroll. Other components of the negative electronic pathway aredepicted in Figure IA. Typically, though not necessarily, these include a current collector disk(often provided with a conductive tab) and a negative cell terminal. In the depictedembodiment, the disk is directly connected to the negative current collector substrate and thecell terminal is directly attached to the current collector disk (often via the conductive tab). Ina cylindrical cell design, the negative cell terminal is usually either a cap or a can.Each of the components of the negative electronic conduction pathway may be characterized byits composition, electrical properties, chemical properties, geometric and structural properties,etc. For example, in certain embodiments, each element of the pathway has the samecomposition (e.g., zinc or zinc coated copper). In other embodiments, at least two of theelements have different compositions.As indicated, an element of the conductive pathway that is the subject of this application is thecarrier or substrate for the negative electrode, which also serves as a current collector. Amongthe criteria to consider when choosing a material and structure for the substrate areelectrochemically compatible with the negativeelectrode materials, cost, ease of coating (with the negative electrode material), suppression ofhydrogen evolution, and ability to facilitate electron transport between the electrochemicallyactive electrode material and the current collector.As explained, the current collection substrate can be provided in various structural formsincluding perforated metal sheets, expanded metals, metal foams, etc. In a specificembodiment, the substrate is a perforated sheet or an expanded metal made from a zinc basedmaterial such as zinc coated copper or zinc coated copper alloy. In certain embodiments, thesubstrate is a perforated sheet having a thickness between about 2 and 5 mils. In certainembodiments, the substrate is an expanded metal having a thickness between about 2 and 20

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mils. In other embodiments, the substrate is a metal foam having a thickness of between about15 and 60 mils. In a specific embodiment, the carrier is about 3-4 mils thick perforated zinccoated copper. A specific range for the thickness of the negative electrode, including the carriermetal and negative electrode material is about 10 to 24 mils. Other components of thenegative pathway, such as a negative current collector disk and cap, may be made from any ofthe base metals identified above for the current collection substrate. The base material chosenfor the disk and/or cap should be highly conductive and inhibit the evolution of hydrogen, etc.In certain embodiments, one or both of the disk and the cap employs zinc or a zinc alloy as abase metal. In certain embodiments, the current collector disk and/or the cap is a copper orcopper alloy coated with zinc or an alloy of zinc containing, e.g., tin, silver, indium, lead, or acombination thereof. It may be desirable to pre-weld the current collector disk and jelly roll oremploy a jelly roll that is an integral part of the current collector disk and tab that could bedirectly welded to the top. Such embodiments may find particular value in relatively low rateapplications. These embodiments are particularly useful when the collector disk contains zinc.The jelly roll may include a tab welded to one side of the negative electrode to facilitatecontact with the collector disk.It has been found that regular vent caps without proper anti-corrosion plating (e.g., tin, lead,silver, zinc, indium, etc.) can cause zinc to corrode during storage, resulting in leakage,gassing, and reduced shelf life. Note that if it is the can, rather than the cap, that is used asthe negative terminal, then the can may be constructed from the materials identified above.In some cases, the entire negative electronic pathway (including the terminal and one or morecurrent collection elements) is made from the same material, e.g.,zinc or copper coated with zinc. In a specific embodiment, the entire electronic pathway fromthe negative electrode to the negative terminal (current collector substrate, current collectordisk, tab, and cap) is zinc plated copper or brass.Some details of the structure of a vent cap and current collector disk, as well as the carriersubstrate itself, are found in the following patent applications which are incorporated herein byreference for all purposes: PCT/US2006/015807 filed April25, 2006 and PCT/US2004/026859 filed August 17, 2004 (publication WO2005/020353 A3).The Positive Electrode The positive electrode generally includes an electrochemically activenickel oxide or hydroxide and one or more additives to facilitate manufacturing, electrontransport, wetting, mechanical properties, etc. For example, a positive electrode formulationmay include at least an electrochemically active nickel oxide or hydroxide (e.g., nickelhydroxide (Ni(0H)2)), zinc oxide, cobalt oxide (CoO), cobalt metal, nickel metal, and a flowcontrol agent such as carboxymethyl cellulose (CMC). Note that the metallic nickel and cobaltmay be chemically pure or alloys. In certain embodiments, the positive electrode has acomposition similar to that employed to fabricate the nickel electrode in a conventional nickelcadmium battery, although there may be some important optimizations for the nickel zincbattery system. A nickel foam matrix is preferably used to support the electroactive nickel(e.g., Ni(OH)2) electrode material. In one example, commercially available nickel foam byInco, Ltd. may be used. The diffusion path to the Ni(OH)2 (or other electrochemically activematerial) through the nickel foam should be short for applications requiring high dischargerates. At high rates, the time it takes ions to penetrate the nickel foam is important. The widthof the positive electrode, comprising nickel foam filled with the Ni(OH)2 (or otherelectrochemically active material) and other electrode materials, should be optimized so thatthe nickel foam provides sufficient void space for the Ni(OH)2 material while keeping thediffusion path of the ions to the Ni(OH)2 through the foam short. The foam substrate thicknessmay be may be between 15 and 60 mils. In a preferred embodiment, the thickness of thepositive electrode, comprising nickel foam filled with the electrochemically active and otherelectrode materials, ranges from about 16 - 24 mils. In a particularly preferred embodiment,positive electrode is about 20 mils thick.The density of the nickel foam should be optimized to ensure that theelectrochemically active material uniformly penetrates the void space of the foam. In apreferred embodiment, nickel foam of density ranging from about 300 - 500 g/m2 is used. Aneven more preferred range is between about 350 - 500 g/m2. In a particularly preferredembodiment nickel foam of density of about 350 g/m2 is used. As the width of the electrodelayer is decreased, the foam may be made less dense to ensure there is sufficient void space.In a preferred embodiment, a nickel foam density of about 350 g/m2 and thickness rangingfrom about 16 - 18 mils is used.The SeparatorA separator serves to mechanically isolate the positive and negative electrodes, while allowingionic exchange to occur between the electrodes and the electrolyte. The separator also blockszinc dendrite formation. Dendrites are crystalline structures having a skeletal or tree-likegrowth pattern ("dendritic growth") in metal deposition. In practice, dendrites form in the

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conductive media of a power cell during the lifetime of the cell and effectively bridge thenegative and positive electrodes causing shorts and subsequent loss of battery function.Typically, a separator will have small pores. In certain embodiments described herein, theseparator includes multiple layers. The pores and/or laminate structure may provide a tortuouspath for zinc dendrites and therefore effectively bar penetration and shorting by dendrites.Preferably, the porous separator has a tortuosity of between about 1.5 and 10, more preferablybetween about 2 and 5. The average pore diameter is preferably at most about 0.2 microns,and more preferably between about 0.02 and 0.1 microns. Also, the pore size is preferablyfairly uniform in the separator. In a specific embodiment, the separator has a porosity ofbetween about 35 and 55% with one preferred material having 45% porosity and a pore size of0.1 micron.In a preferred embodiment, the separator comprises at least two layers (and preferably exactlytwo layers) - a barrier layer to block zinc penetration and a wetting layer to keep the cell wetwith electrolyte, allowing ionic exchange. This is generally not the case with nickel cadmiumcells, which employ only a single separator material between adjacent electrode layers.Performance of the cell may be aided by keeping the positive electrode as wet as possible andthe negative electrode relatively dry. Thus, in some embodiments, the barrier layer is locatedadjacent to the negative electrode and the wetting layer is located adjacent to the positiveelectrode. This arrangement improves performance ofthe cell by maintaining electrolyte in intimate contact with the positive electrode.In other embodiments, the wetting layer is placed adjacent to the negative electrode and thebarrier layer is placed adjacent to the positive electrode. This arrangement aids recombinationof oxygen at the negative electrode by facilitating oxygen transport to the negative electrodevia the electrolyte.The barrier layer is typically a microporous membrane. Any microporous membrane that isionically conductive may be used. Often a polyolefin having a porosity of between about 30 and80 per cent, and an average pore size of between about 0.005 and 0.3 micron will be suitable.In a preferred embodiment, the barrier layer is a microporous polypropylene. The barrier layeris typically about 0.5 - 4 mils thick, more preferably between about 1.5 and 4 mils thick.The wetting layer may be made of any suitable wettable separator material. Typically thewetting layer has a relatively high porosity e.g., between about 50 and 85% porosity. Examplesinclude polyamide materials such as nylon-based as well as wettable polyethylene andpolypropylene materials. In certain embodiments, the wetting layer is between about 1 and 10mils thick, more preferably between about 3 and 6 mils thick. Examples of separate materialsthat may be employed as the wetting material include NKK VLlOO (NKK Corporation, Tokyo,Japan), Freudenberg FS2213E, Scimat 650/45 (SciMAT Limited, Swindon, UK), and VileneFV4365. Other separator materials known in the art may be employed. As indicated,nylon-based materials and microporous polyolefins (e.g., polyethylenes and polypropylenes) arevery often suitable.The ElectrolyteThe electrolyte should possess a composition that limits dendrite formation and other forms ofmaterial redistribution in the zinc electrode. Such electrolytes have generally eluded the art.But one that appears to meet the criterion is described in U.S. Patent No. 5,215,836 issued toM. Eisenberg on June 1, 1993, which is hereby incorporated by reference. A particularlypreferred electrolyte includes (1) an alkali or earth alkali hydroxide present in an amount toproduce a stoichiometric excess of hydroxide to acid in the range of about 2.5 to 11 equivalentsper liter, (2) a soluble alkali or earth alkali fluoride in an amount corresponding to aconcentration range of about 0.01 to 1 equivalents per liter of total solution, and (3) a borate,arsenate, and/or phosphate salt (e.g., potassium borate, potassium metaborate, sodiumborate, sodium metaborate, and/or a sodium or potassium phosphate). In one specificembodiment,the electrolyte comprises about 4.5 to 10 equiv/liter of potassium hydroxide, from about 2 to 6equiv/liter boric acid or sodium metaborate and from about 0.01 to 1 equivalents of potassiumfluoride. A specific preferred electrolyte for high rate applications comprises about 8.5equiv/liter of hydroxide, about 4.5 equivalents of boric acid and about 0.2 equivalents ofpotassium fluoride.The invention is not limited to the electrolyte compositions presented in the Eisenberg patent.Generally, any electrolyte composition meeting the criteria specified for the applications ofinterest will suffice. Assuming that high power applications are desired, then the electrolyteshould have very good conductivity. Assuming that long cycle life is desired, then theelectrolyte should resist dendrite formation. In the present invention, the use of borate and/orfluoride containing KOH electrolyte along with appropriate separator layers reduces theformation of dendrites thus achieving a more robust and long-lived power cell.In a specific embodiment, the electrolyte composition includes an excess of between about 3and 5 equiv/liter hydroxide (e.g., KOH, NaOH, and/or LiOH). This assumes that the negativeelectrode is a zinc oxide based electrode. For calcium zincate negative electrodes, alternateelectrolyte formulations may be appropriate. In one example, an appropriate electrolyte for

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calcium zincate has the following composition: about 15 to 25% by weight KOH, about 0.5 to5.0% by weight LiOH. According to various embodiments, the electrolyte may comprise a liquidand a gel. The gel electrolyte may comprise a thickening agent such as CARBOPOL® availablefrom Noveon of Cleveland, OH. In a preferred embodiment, a fraction of the active electrolytematerial is in gel form. In a specific embodiment, about 5-25% by weight of the electrolyte isprovided as gel and the gel component comprises about 1-2% by weight CARBOPOL®.In some cases, the electrolyte may contain a relatively high concentration of phosphate ion asdiscussed in US Patent Application No. 11/346,861, filed February 1, 2006 and incorporatedherein by reference for all purposes.Although various details have been omitted for clarity's sake, various design alternatives maybe implemented. Therefore, the present examples are to be considered as illustrative and notrestrictive, and the invention is not to be limited to the details given herein, but may bemodified within the scope of the invention.

2008036948 ClaimsWhat is claimed is:1. A method of charging a nickel-zinc battery comprising: measuring a temperature of thebattery, calculating a calculated voltage based on at least the temperature of the battery,charging the battery at a constant current until a measured battery voltage is the same as thecalculated voltage, charging the battery at a calculated voltage per nickel-zinc cell, andstopping the battery charging at the calculated voltage per cell when an end-of- chargecondition is satisfied; wherein the battery comprises one or more cells.2. The method of claim 1, wherein the constant current is about 1-2 amps per 2 Amp hour ofcapacity in the battery. 3. The method of claim 1, wherein the constant current chargingoperation increases a capacity of the battery to about 80%.4. The method of claim 1, further comprising: charging the battery at a corrective current tocorrect cell imbalance after charging the battery at the calculated voltage. 5. The method ofclaim 1, further comprising: charging the battery at a minimum current to maintain chargeduring period when the battery is not in use and the end-of-charge condition has been satisfied.6. The method of claim 1, further comprising: charging the battery at an initial current until astart-of-charge condition is satisfied. 7. The method of claim 4, wherein the corrective currentis about 50-200 milliamps per 2 Amp hour of capacity in the battery.8. The method of claim 5, wherein the minimum current is about 0-50 milliamps per 2 Amphour of capacity in the battery.9. The method of claim 6, wherein the initial current is about 0-50 milliamps per 2 Amp hour ofcapacity in the battery.10. The method of claim 1, wherein the end-of-charge condition is selected from the groupconsisting of: a charging current of less than a defined current associated with a specifiedstate-of- charge; a lapse of 1.5 hours of charging at the calculated voltage; a batterytemperature increase of 15 degrees Celsius; a charging current of more than about a definedthreshold associated with a short circuit in the batery; and, combinations thereof.11. The method of claim 6, wherein the start-of charge condition is selected from the groupconsisting of:(a) a battery temperature of 15 degrees Celsius; (b) a battery voltage of about 1 volt per cell;and,(c) a lapse of about 20 hours or more without meeting either of conditions (a) or (b).12. The method of claim 1, further comprising repeating the measuring, and calculating duringthe charging.13. A nickel-zinc battery charger comprising: an enclosure for holding the nickel-zinc battery, athermistor configured to thermally couple to a battery during operation; and, a controllerconfigured to execute a set of instructions, the instructions comprising instructions to: measurea temperature of the battery, calculate a calculated voltage, charge the battery at a constantcurrent until a measured battery voltage equals the calculated voltage,charge the battery at the calculated voltage, and stop the charge at the calculated voltage whenan end-of-charge condition is detected.14. The battery charger of claim 13, further comprising: a recondition button and wherein theinstructions further comprises charging the battery at an initial current when the reconditionbutton is pressed.15. The battery charger of claim 13, wherein the instructions further comprises instructions tocharge the battery at a corrective current. 16. The battery charger of claim 13, wherein theinstructions further comprises instructions to charge the battery at a minimum current.17. A method of correcting nickel-zinc battery cell imbalance comprising: providing a batterypack at greater than about 90% state-of-charge in a charger, and charging the battery at acorrective current for about 30 minutes to 2 hours without limiting the voltage.18. The method of claim 17, wherein the corrective current is about 50-200 milliamps per 2

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Amp hour of capacity in the battery. 19. The method of claim 17, further comprising: chargingthe battery at a minimum current until the battery is removed from the charger.20. The method of claim 19, wherein the minimum current is 0-50 milliamps per 2 Amp hour ofcapacity in the battery. 21. A method of charging a battery comprising: measuring atemperature of the battery, measuring a voltage of the battery, calculating a calculated voltagebased on at least the temperature of the battery,charging the battery at a charge current until the battery voltage equals the calculated voltage,reducing the charging current by a defined factor, charging the battery at the reduced chargecurrent until the battery voltage equals the calculated voltage, wherein the factor is about 2-10.22. The method of claim 21, further comprising repeating the reducing and charging the batteryat the reduced charge operations to the same voltage level. 23. A method of charging anickel-zinc cell, the method comprising:(a) charging the nickel-zinc battery at a constant current until reaching a point at which (i) thecell's state of charge is at least about 70%, (ii) a nickel electrode of the cell has not yet begunto evolve oxygen at a substantial level, and (iii) the cell voltage is between about 1.88 and1.93 volts; and (b) charging the nickel-zinc battery at a constant voltage in the range of1.88-1.93 until an end-of-charge condition is satisfied.24. The method of claim 23, wherein charging the battery at a constant current is conducted ata current of up to about 4 Amps per 2 Amp hour battery capacity, and wherein the nickel-zincbattery employs an electrolyte having a conductivity of at least about 0.5 cm"1 ohm ~\25. The method of claim 24, wherein charging t he battery at a constant current is conducteduntil the cell voltage is between about 1.88 and 1.91 volts.

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DEP

ARTMENT OF JUSTICE

OF

FIC

EOF JUSTICE PRO

GR

AM

S

BJA

NIJ

OJJ DP BJSO

VC

U.S. Department of Justice

Office of Justice Programs

National Institute of Justice

National Institute of JusticeLaw Enforcement and Corrections Standards and Testing Program

NEW TECHNOLOGY BATTERIES GUIDE

NIJ Guide 200-98

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The National Institute of Justice is a component of the Office of JusticePrograms, which also includes the Bureau of Justice Assistance, Bureau ofJustice Statistics, Office of Juvenile Justice and Delinquency Prevention, andthe Office for Victims of Crime.

ABOUT THE LAW ENFORCEMENT AND CORRECTIONS STANDARDS AND TESTING PROGRAM

The Law Enforcement and Corrections Standards and Testing Program is sponsored by the Office of Science andTechnology of the National Institute of Justice (NIJ), U.S. Department of Justice. The program responds to the mandateof the Justice System Improvement Act of 1979, which created NIJ and directed it to encourage research anddevelopment to improve the criminal justice system and to disseminate the results to Federal, State, and local agencies.

The Law Enforcement and Corrections Standards and Testing Program is an applied research effort thatdetermines the technological needs of justice system agencies, sets minimum performance standards for specific devices,tests commercially available equipment against those standards, and disseminates the standards and the test results tocriminal justice agencies nationally and internationally.

The program operates through:The Law Enforcement and Corrections Technology Advisory Council (LECTAC) consisting of nationally

recognized criminal justice practitioners from Federal, State, and local agencies, which assesses technological needsand sets priorities for research programs and items to be evaluated and tested.

The Office of Law Enforcement Standards (OLES) at the National Institute of Standards and Technology, whichdevelops voluntary national performance standards for compliance testing to ensure that individual items of equipmentare suitable for use by criminal justice agencies. The standards are based upon laboratory testing and evaluation ofrepresentative samples of each item of equipment to determine the key attributes, develop test methods, and establishminimum performance requirements for each essential attribute. In addition to the highly technical standards, OLESalso produces technical reports and user guidelines that explain in nontechnical terms the capabilities of availableequipment.

The National Law Enforcement and Corrections Technology Center (NLECTC), operated by a grantee, whichsupervises a national compliance testing program conducted by independent laboratories. The standards developed byOLES serve as performance benchmarks against which commercial equipment is measured. The facilities, personnel,and testing capabilities of the independent laboratories are evaluated by OLES prior to testing each item of equipment,and OLES helps the NLECTC staff review and analyze data. Test results are published in Equipment PerformanceReports designed to help justice system procurement officials make informed purchasing decisions.

Publications are available at no charge from the National Law Enforcement and Corrections Technology Center.Some documents are also available online through the Internet/World Wide Web. To request a document or additionalinformation, call 800-248-2742 or 301-519-5060, or write:

National Law Enforcement and Corrections Technology CenterP.O. Box 1160Rockville, MD 20849-1160E-mail: [email protected] Wide Web address: http://www.nlectc.org

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National Institute of Justice

Jeremy TravisDirector

The Technical effort to develop this Guide was conductedunder Interagency Agreement 94-IJ-R-004

Project No. 97-027-CTT.

This Guide was prepared by the Office of Law Enforcement Standards (OLES) of the

National Institute of Standards and Technology (NIST)under the direction of A. George Lieberman,

Program Manager for Communications Systems,and Kathleen M. Higgins, Director of OLES.

The work resulting in this guide was sponsored bythe National Institute of Justice, David G. Boyd,

Director, Office of Science and Technology.

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iii

FOREWORD

The Office of Law Enforcement Standards (OLES) of the National Institute of Standardsand Technology furnishes technical support to the National Institute of Justice program tostrengthen law enforcement and criminal justice in the United States. OLES’s function is toconduct research that will assist law enforcement and criminal justice agencies in the selectionand procurement of quality equipment.

OLES is: (1) subjecting existing equipment to laboratory testing and evaluation, and (2)conducting research leading to the development of several series of documents, includingnational standards, user guides, and technical reports.

This document covers research conducted by OLES under the sponsorship of the NationalInstitute of Justice. Additional reports as well as other documents are being issued under theOLES program in the areas of protective clothing and equipment, communications systems,emergency equipment, investigative aids, security systems, vehicles, weapons, and analyticaltechniques and standard reference materials used by the forensic community.

Technical comments and suggestions concerning this report are invited from all interestedparties. They may be addressed to the Director, Office of Law Enforcement Standards, NationalInstitute of Standards and Technology, Gaithersburg, MD 20899.

David G. Boyd, Director Office of Science and Technology National Institute of Justice

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iv

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v

A standard is not intended to informand guide the reader; that is the

function of a guideline

BACKGROUND

The Office of Law Enforcement Standards(OLES) was established by the NationalInstitute of Justice (NIJ) to provide focus on twomajor objectives: (1) to find existing equipmentwhich can be purchased today, and (2) todevelop new law-enforcement equipment whichcan be made available as soon as possible. Apart of OLES’s mission is to become thoroughlyfamiliar with existing equipment, to evaluate itsperformance by means of objective laboratorytests, to develop andimprove thesemethods of test, todevelop performancestandards forselected equipmentitems, and to prepareguidelines for theselection and use ofthis equipment. All of these activities aredirected toward providing law enforcementagencies with assistance in making goodequipment selections and acquisitions inaccordance with their own requirements.

As the OLES program has matured, there hasbeen a gradual shift in the objectives of theOLES projects. The initial emphasis on thedevelopment of standards has decreased, and theemphasis on the development of guidelines hasincreased. For the significance of this shift inemphasis to be appreciated, the precisedefinitions of the words “standard” and“guideline” as used in this context must beclearly understood.

A “standard” for a particular item of equipmentis understood to be a formal document, in a

conventional format, that details theperformance that the equipment is required togive, and describes test methods by which itsactual performance can be measured. Theserequirements are technical, and are stated interms directly related to the equipment’s use.The basic purposes of a standard are (1) to be areference in procurement documents created bypurchasing officers who wish to specifyequipment of the “standard” quality, and (2) to

identify objectivelyequipment ofacceptableperformance.

Note that a standardis not intended toinform and guide thereader; that is the

function of a “guideline.” Guidelines are writtenin non-technical language and are addressed tothe potential user of the equipment. Theyinclude a general discussion of the equipment,its important performance attributes, the variousmodels currently on the market, objective testdata where available, and any other informationthat might help the reader make a rationalselection among the various options oralternatives available to him or her.

This battery guide is provided to inform thereader of the latest technology related to batterycomposition, battery usage, and battery chargingtechniques.

Kathleen HigginsNational Institute of Standards and Technology

March 27, 1997

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CONTENTS

page

FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

CONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii

List of Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . viii

1. Fundamentals of Battery Technology. . . . . . . . . . 11.1 What is a Battery?. . . . . . . . . . . . . . . . . . . . . 11.2 How Does a Battery Work?. . . . . . . . . . . . . . 11.3 Galvanic Cells vs. Batteries. . . . . . . . . . . . . . 31.4 Primary Battery. . . . . . . . . . . . . . . . . . . . . . . 31.5 Secondary Battery. . . . . . . . . . . . . . . . . . . . . 31.6 Battery Labels. . . . . . . . . . . . . . . . . . . . . . . . 3

2. Available Battery Types. . . . . . . . . . . . . . . . . . . . 52.1 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.1.1 Acid vs. Alkaline. . . . . . . . . . . . . . . . . 52.1.2 Wet vs. Dry. . . . . . . . . . . . . . . . . . . . . 52.1.3 Categories. . . . . . . . . . . . . . . . . . . . . . 5

2.2 Vehicular Batteries. . . . . . . . . . . . . . . . . . . . 62.2.1 Lead-Acid . . . . . . . . . . . . . . . . . . . 62.2.2 Sealed vs. Flooded. . . . . . . . . . . . . . . 62.2.3 Deep-Cycle Batteries. . . . . . . . . . . . . . 72.2.4 Battery Categories for Vehicular

Batteries. . . . . . . . . . . . . . . . . . . . . . . . 72.3 “Household” Batteries. . . . . . . . . . . . . . . . . . 7

2.3.1 Zinc-carbon (Z-C). . . . . . . . . . . . . . . . 82.3.2 Zinc-Manganese Dioxide Alkaline Cells

(“Alkaline Batteries”) . . . . . . . . . . . . . 82.3.3 Rechargeable Alkaline Batteries. . . . . 92.3.4 Nickel-Cadmium (Ni-Cd). . . . . . . . . . 92.3.5 Nickel-Metal Hydride (Ni-MH) . . . . 102.3.6 Nickel-Iron (Ni-I) . . . . . . . . . . . . . . . 10

2.3.7 Nickel-Zinc (Ni-Z) . . . . . . . . . . . . . . 102.3.8 Lithium and Lithium Ion. . . . . . . . . . 10

2.4 Specialty Batteries (“Button” and MiniatureBatteries). . . . . . . . . . . . . . . . . . . . . . . . . . . . 122.4.1 Metal-Air Cells. . . . . . . . . . . . . . . . . 122.4.2 Silver Oxide . . . . . . . . . . . . . . . . . . . 122.4.3 Mercury Oxide. . . . . . . . . . . . . . . . . 13

2.5 Other Batteries. . . . . . . . . . . . . . . . . . . . . . . 132.5.1 Nickel-Hydrogen (Ni-H). . . . . . . . . . 132.5.2 Thermal Batteries. . . . . . . . . . . . . . . 132.5.3 Super Capacitor. . . . . . . . . . . . . . . . . 132.5.4 The Potato Battery. . . . . . . . . . . . . . . 142.5.5 The Sea Battery. . . . . . . . . . . . . . . . . 142.5.6 Other Developments. . . . . . . . . . . . . 14

3. Performance, Economics and Tradeoffs. . . . . . . 153.1 Energy Densities. . . . . . . . . . . . . . . . . . . . . 153.2 Energy per Mass. . . . . . . . . . . . . . . . . . . . . 153.3 Energy Per Volume. . . . . . . . . . . . . . . . . . . 153.4 Memory Effects. . . . . . . . . . . . . . . . . . . . . . 163.5 Voltage Profiles. . . . . . . . . . . . . . . . . . . . . . 163.6 Self-Discharge Rates. . . . . . . . . . . . . . . . . . 173.7 Operating Temperatures. . . . . . . . . . . . . . . 173.8 Cycle Life . . . . . . . . . . . . . . . . . . . . . . . . . . 183.9 Capacity Testing. . . . . . . . . . . . . . . . . . . . . 183.10 Battery Technology Comparison. . . . . . . . 18

4. Selecting the Right Battery for the Application . 234.1 Battery Properties. . . . . . . . . . . . . . . . . . . . 244.2 Environmental Concerns. . . . . . . . . . . . . . . 244.3 Standardization. . . . . . . . . . . . . . . . . . . . . . 264.4 Testing Capacities. . . . . . . . . . . . . . . . . . . . 264.5 Mobile Radios. . . . . . . . . . . . . . . . . . . . . . . 274.6 Cellular Phones and PCS Phones. . . . . . . . 274.7 Laptop Computers. . . . . . . . . . . . . . . . . . . . 284.8 Camcorders. . . . . . . . . . . . . . . . . . . . . . . . . 284.9 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . 29

5. Battery Handling and Maintenance. . . . . . . . . . . 315.1 Battery Dangers. . . . . . . . . . . . . . . . . . . . . . 315.2 Extending Battery Life. . . . . . . . . . . . . . . . 33

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6. Battery Chargers and Adapters. . . . . . . . . . . . . . 356.1 Battery Chargers. . . . . . . . . . . . . . . . . . . . . 356.2 Charge Rates. . . . . . . . . . . . . . . . . . . . . . . . 366.3 Charging Techniques. . . . . . . . . . . . . . . . . . 366.4 Charging Lead-Acid Batteries. . . . . . . . . . . 366.5 Charging Ni-Cd Batteries. . . . . . . . . . . . . . 376.6 Timed-Charge Charging. . . . . . . . . . . . . . . 376.7 Pulsed Charge-Discharge Chargers. . . . . . . 386.8 Charging Button Batteries. . . . . . . . . . . . . . 386.9 Internal Chargers. . . . . . . . . . . . . . . . . . . . . 386.10 Battery Testers. . . . . . . . . . . . . . . . . . . . . . 386.11 “Smart” Batteries. . . . . . . . . . . . . . . . . . . . 396.12 End of Life . . . . . . . . . . . . . . . . . . . . . . . . 396.13 Battery Adapters. . . . . . . . . . . . . . . . . . . . 40

7. Products and Suppliers. . . . . . . . . . . . . . . . . . . . 417.1 Battery Manufacturers. . . . . . . . . . . . . . . . . 41

7.1.1 Battery Engineering. . . . . . . . . . . . . . 427.1.2 Duracell. . . . . . . . . . . . . . . . . . . . . . . 427.1.3 Eveready. . . . . . . . . . . . . . . . . . . . . . 427.1.4 Rayovac. . . . . . . . . . . . . . . . . . . . . . . 42

8. A Glossary of Battery Terms. . . . . . . . . . . . . . . 43

9. Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

List of Figurespage

Figure 1. Conceptual diagram of a galvanic cell. . . . 1Figure 2. Energy densities, W#h/kg, of various battery

types (adapted from NAVSO P-3676).. . . . . . . 15Figure 3. Energy densities, W#h/L, of various battery

types (adapted from NAVSO P-3676).. . . . . . . 16Figure 4. Flat discharge curve vs. sloping discharge

curve. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Figure 5. Performance comparison of primary and

secondary alkaline and Ni-Cd batteries (adaptedfrom Design Note: Renewable Reusable AlkalineBatteries). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

List of Tablespage

Table 1. The Electromotive Series for Some BatteryComponents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Table 2. Various Popular Household-Battery Sizes . 8Table 3. Battery Technology Comparison (adapted from

Design Note: Renewable Reusable AlkalineBatteries) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Table 4. A Comparison of Several Popular BatteryTypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Table 5. Recommended Battery Types for VariousUsage Conditions. . . . . . . . . . . . . . . . . . . . . . . . 25

Table 6. Typical Usage of PortableTelecommunications Equipment.. . . . . . . . . . . . 27

Table 7. Charge Rate Descriptions. . . . . . . . . . . . . 35Table 8. Some On-Line Information Available via the

World Wide Web . . . . . . . . . . . . . . . . . . . . . . . . 41

List of Equationspage

Equation 1. The chemical reaction in a lead-acidbattery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Equation 2. The chemical reaction in a Leclanché cell.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Equation 3. The chemical reaction in a nickel-cadmium battery.. . . . . . . . . . . . . . . . . . . . . . . . . 9

Equation 4. The chemical reaction in a lithium-manganese dioxide cell.. . . . . . . . . . . . . . . . . . . 11

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COMMONLY USED SYMBOLS AND ABBREVIATIONS

A ampere H henry nm nanometerac alternating current h hour No. numberAM amplitude modulation hf high frequency o.d. outside diametercd candela Hz hertz (c/s) 6 ohmcm centimeter i.d. inside diameter p. pageCP chemically pure in inch Pa pascalc/s cycle per second ir infrared pe probable errord day J joule pp. pagesdB decibel L lambert ppm part per milliondc direct current L liter qt quart(C degree Celsius lb pound rad radian(F degree Fahrenheit lbf pound-force rf radio frequencydia diameter lbf#in pound-force inch rh relative humidityemf electromotive force lm lumen s secondeq equation ln logarithm (natural) SD standard deviationF farad log logarithm (common) sec. sectionfc footcandle M molar SWR standing wave ratiofig. figure m meter uhf ultrahigh frequencyFM frequency modulation min minute uv ultravioletft foot mm millimeter V voltft/s foot per second mph mile per hour vhf very high frequencyg acceleration/gravity m/s meter per second W wattg gram N newton � wavelengthgr grain N#m newton meter wt weight

area=unit2 (e.g., ft2, in2, etc.); volume=unit3 (e.g., ft2, m3, etc.)

PREFIXES

d deci (10-1) da deka (10)c centi (10-2) h hecto (102)m milli (10-3) k kilo (103)µ micro (10-6) M mega (106)n nano (10-9) G giga (109)p pico (10-12) T tera (1012)

COMMON CONVERSIONS (See ASTM E380)

ft/s×0.3048000=m/s lb×0.4535924=kgft×0.3048=m lbf×4.448222=Nft#lbf×1.355818=J lbf/ft×14.59390=N/mgr×0.06479891=g lbf#in×0.1129848=N##min×2.54=cm lbf/in2×6894.757=PakWh×3600000=J mph1.609344=km/h

qt×0.9463529=L

Temperature: (T(F�32)×5/9=T

(C

Temperature: (T(C×C9/5)+32=T

(F

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Figure 1. Conceptual diagram of a galvanic cell.

1. Fundamentals of Battery Technology

1.1 WHAT IS A BATTERY ?

A battery, in concept, can be any device thatstores energy for later use. A rock, pushed tothe top of a hill, can be considered a kind ofbattery, since the energy used to push it up thehill (chemical energy, from muscles orcombustion engines) is converted and storedas potential kinetic energy at the top of thehill. Later, that energy is released as kineticand thermal energy when the rock rolls downthe hill.

Common use of theword, “battery,”however, is limitedto an electro-chemical devicethat convertschemical energyinto electricity, byuse of a galvaniccell. A galvanic cellis a fairly simpledevice consisting oftwo electrodes (ananode and acathode) and anelectrolyte solution. Batteries consist of one ormore galvanic cells.

1.2 HOW DOES A BATTERY WORK?

Figure 1 shows a simple galvanic cell.Electrodes (two plates, each made from adifferent kind of metal or metallic compound)are placed in an electrolyte solution. External

wires connect the electrodes to an electricalload (a light bulb in this case). The metal inthe anode (the negative terminal) oxidizes(i.e., it “rusts”), releasing negatively chargedelectrons and positively charged metal ions.The electrons travel through the wire (and theelectrical load) to the cathode (the positiveterminal). The electrons combine with thematerial in the cathode. This combinationprocess is called reduction, and it releases anegatively charged metal-oxide ion. At the

interface with theelectrolyte, this ioncauses a watermolecule to splitinto a hydrogen ionand a hydroxideion. The positivelycharged hydrogenion combines withthe negativelycharged metal-oxide ion andbecomes inert. Thenegatively chargedhydroxide ionflows through theelectrolyte to the

anode where it combines with the positivelycharged metal ion, forming a water moleculeand a metal-oxide molecule.

In effect, metal ions from the anode will“dissolve” into the electrolyte solution whilehydrogen molecules from the electrolyte aredeposited onto the cathode.

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Anode Materials(Listed from worst

[most positive] to best[most negative])

Cathode Materials(Listed from best[most positive] to

worst [most negative])

Gold Ferrate

Platinum Iron Oxide

Mercury Cuprous Oxide

Palladium Iodate

Silver Cupric Oxide

Copper Mercuric Oxide

Hydrogen Cobaltic Oxide

Lead Manganese Dioxide

Tin Lead Dioxide

Nickel Silver Oxide

Iron Oxygen

Chromium Nickel Oxyhydroxide

Zinc Nickel Dioxide

Aluminum Silver Peroxide

Magnesium Permanganate

Lithium Bromate

Table 1. The Electromotive Series for SomeBattery Components

When the anode is fully oxidized or thecathode is fully reduced, the chemical reactionwill stop and the battery is considered to bedischarged.

Recharging a battery is usually a matter ofexternally applying a voltage across the platesto reverse the chemical process. Somechemical reactions, however, are difficult orimpossible to reverse. Cells with irreversiblereactions are commonly known as primarycells, while cells with reversible reactions areknown as secondary cells. It is dangerous toattempt to recharge primary cells.

The amount of voltage and current that agalvanic cell produces is directly related to thetypes of materials used in the electrodes andelectrolyte. The length of time the cell canproduce that voltage and current is related tothe amount of active material in the cell andthe cell’s design.

Every metal or metal compound has anelectromotive force, which is the propensity ofthe metal to gain or lose electrons in relationto another material. Compounds with apositive electromotive force will make goodanodes and those with a negative force willmake good cathodes. The larger the differencebetween the electromotive forces of the anodeand cathode, the greater the amount of energythat can be produced by the cell. Table 1shows the electromotive force of somecommon battery components. Over the years, battery specialists have

experimented with many differentcombinations of material and have generallytried to balance the potential energy output ofa battery with the costs of manufacturing thebattery. Other factors, such as battery weight,shelf life, and environmental impact, alsoenter into a battery’s design.

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A battery is one or more galvaniccells connected in series or in

parallel

1.3 GALVANIC CELLS VS. BATTERIES

From earlier discussion, we know that abattery is one or more galvanic cells connectedin series or in parallel.

A battery composed of two 1.5 V galvaniccells connected in series, for example, willproduce 3 V. A typical 9 V battery is simplysix 1.5 V cells connected in series. Such aseries battery, however, will produce a currentthat is the equivalent to just one of thegalvanic cells.

A battery composed of two 1.5 V galvaniccells connected in parallel, on the other hand,will still produce avoltage of 1.5 V,but the currentprovided can bedouble the currentthat just one cellwould create. Sucha battery canprovide current twice as long as a single cell.

Many galvanic cells can be thus connected tocreate a battery with almost any current at anyvoltage level.

1.4 PRIMARY BATTERY

A primary battery is a battery that is designedto be cycled (fully discharged) only once andthen discarded. Although primary batteries areoften made from the same base materials assecondary (rechargeable) batteries, the designand manufacturing processes are not the same.

Battery manufacturers recommend thatprimary batteries not be recharged. Althoughattempts at recharging a primary battery willoccasionally succeed (usually with a

diminished capacity), it is more likely that thebattery will simply fail to hold any charge, willleak electrolyte onto the battery charger, orwill overheat and cause a fire. It is unwise anddangerous to recharge a primary battery.

1.5 SECONDARY BATTERY

A secondary battery is commonly known as arechargeable battery. It is usually designed tohave a lifetime of between 100 and 1000recharge cycles, depending on the compositematerials.

Secondary batteries are, generally, more costeffective over time than primary batteries,

since the batterycan be rechargedand reused. Asingle dischargecycle of a primarybattery, however,will provide morecurrent for a longer

period of time than a single discharge cycle ofan equivalent secondary battery.

1.6 BATTERY LABELS

The American National Standards Institute(ANSI) Standard, ANSI C18.1M-1992, listsseveral battery features that must be listed on abattery’s label. They are:

_ Manufacturer -- The name of the batterymanufacturer._ ANSI Number -- The ANSI/NEDAnumber of the battery._ Date -- The month and year that the batterywas manufactured or the month and year thatthe battery “expires” (i.e., is no longerguaranteed by the manufacturer)._ Voltage -- The nominal battery voltage.

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_ Polarity -- The positive and negativeterminals. The terminals must be clearlymarked._ Warnings -- Other warnings and cautionsrelated to battery usage and disposal.

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2. Available Battery Types

2.1 GENERAL

2.1.1 Acid vs. AlkalineBatteries are often classified by the type ofelectrolyte used in their construction. Thereare three common classifications: acid, mildlyacid, and alkaline.

Acid-based batteries often use sulphuric acidas the major component of the electrolyte.Automobile batteries are acid-based. Theelectrolyte used in mildly acidic batteries is farless corrosive than typical acid-based batteriesand usually includes a variety of salts thatproduce the desired acidity level. Inexpensivehousehold batteries are mildly acidic batteries.

Alkaline batteries typically use sodiumhydroxide or potassium hydroxide as the maincomponent of the electrolyte. Alkalinebatteries are often used in applications wherelong-lasting, high-energy output is needed,such as cellular phones, portable CD players,radios, pagers, and flash cameras.

2.1.2 Wet vs. Dry“Wet” cells refer to galvanic cells where theelectrolyte is liquid in form and is allowed toflow freely within the cell casing. Wetbatteries are often sensitive to the orientationof the battery. For example, if a wet cell isoriented such that a gas pocket accumulatesaround one of the electrodes, the cell will notproduce current. Most automobile batteries arewet cells.

“Dry” cells are cells that use a solid orpowdery electrolyte. These kind of electrolytesuse the ambient moisture in the air tocomplete the chemical process. Cells withliquid electrolyte can be classified as “dry” ifthe electrolyte is immobilized by somemechanism, such as by gelling it or by holdingit in place with an absorbent substance such aspaper.

In common usage, “dry cell” batteries willusually refer to zinc-carbon cells (Sec. 2.3.1)or zinc-alkaline-manganese dioxide cells(Sec. 2.3.2), where the electrolyte is oftengelled or held in place by absorbent paper.

Some cells are difficult to categorize. Forexample, one type of cell is designed to bestored for long periods without its electrolytepresent. Just before power is needed from thecell, liquid electrolyte is added.

2.1.3 CategoriesBatteries can further be classified by theirintended use. The following sections discussfour generic categories of batteries;“vehicular” batteries (Sec. 2.2), “household”batteries (Sec. 2.3), “specialty” batteries (Sec.2.4), and “other” batteries (Sec. 2.5). Eachsection will focus on the general properties ofthat category of battery.

Note that some battery types (acidic oralkaline, wet or dry) can fall into severaldifferent categories. For this guideline, batterytypes are placed into the category in which

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Battery manufacturing is the singlelargest use for lead in the world.

PbO2�Pb�2H2SO4 ��� 2PbSO4�2H2O

Equation 1. The chemical reaction in a lead-acid battery.

they are most likely to be found in commercialusage.

2.2 VEHICULAR BATTERIES

This section discusses battery types andconfigurations that are typically used in motorvehicles. This category can include batteriesthat drive electric motors directly or those thatprovide starting energy for combustionengines. This category will also include large,stationary batteries used as power sources foremergency building lighting, remote-sitepower, and computer back up.

Vehicular batteriesare usuallyavailable off-the-shelf in standarddesigns or can becustom built forspecificapplications.

2.2.1 Lead-AcidLead-acid batteries,developed in the late 1800s, were the firstcommercially practical batteries. Batteries ofthis type remain popular because they arerelatively inexpensive to produce and sell. Themost widely known uses of lead-acid batteriesare as automobile batteries. Rechargeablelead-acid batteries have become the mostwidely used type of battery in theworld—more than 20 times the use rate of itsnearest rivals. In fact, battery manufacturing isthe single largest use for lead in the world.1

Equation 1 shows the chemical reaction in alead-acid cell.

Lead-acid batteries remain popular becausethey can produce high or low currents over awide range of temperatures, they have goodshelf life and life cycles, and they arerelatively inexpensive to manufacture. Lead-

acid batteries areusuallyrechargeable.

Lead-acid batteriescome in all mannerof shapes and sizes,

from household batteries to large batteries foruse in submarines. The most noticeableshortcomings of lead-acid batteries are theirrelatively heavy weight and their fallingvoltage profile during discharge (Sec. 3.5).

2.2.2 Sealed vs. FloodedIn “flooded” batteries, the oxygen created atthe positive electrode is released from the celland vented into the atmosphere. Similarly, thehydrogen created at the negative electrode isalso vented into the atmosphere. The overallresult is a net loss of water (H2O) from thecell. This lost water needs to be periodicallyreplaced. Flooded batteries must be vented toprevent excess pressure from the build up ofthese gases. Also, the room or enclosurehousing the battery must be vented, since aconcentrated hydrogen and oxygenatmosphere is explosive.

1Encyclopedia of Physical Science andTechnology, Brooke Schumm, Jr., 1992.

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In sealed batteries, however, the generatedoxygen combines chemically with the lead andthen the hydrogen at the negative electrode,and then again with reactive agents in theelectrolyte, to recreate water. The net result isno significant loss of water from the cell.

2.2.3 Deep-Cycle BatteriesDeep-cycle batteries are built in configurationssimilar to those of regular batteries, exceptthat they are specifically designed forprolonged use rather than for short bursts ofuse followed by a short recycling period. Theterm “deep-cycle” is most often applied tolead-acid batteries. Deep-cycle batteriesrequire longer charging times, with lowercurrent levels, than is appropriate for regularbatteries.

As an example, a typical automobile battery isusually used to provide a short, intense burstof electricity to the automobile’s starter. Thebattery is then quickly recharged by theautomobile’s electrical system as the engineruns. The typical automobile battery is not adeep-cycle battery.

A battery that provides power to a recreationalvehicle (RV), on the other hand, would beexpected to power lights, small appliances,and other electronics over an extended periodof time, even while the RV’s engine is notrunning. Deep-cycle batteries are moreappropriate for this type of continual usage.

2.2.4 Battery Categories for VehicularBatteries

Vehicular, lead-acid batteries are furthergrouped (by typical usage) into three differentcategories:

8 Starting-Lighting-Ignition (SLI) --Typically, these batteries are used for short,quick-burst, high-current applications. Anexample is an automotive battery, which isexpected to provide high current, occasionally,to the engine’s starter.8 Traction -- Traction batteries must providemoderate power through many deep dischargecycles. One typical use of traction batteries isto provide power for small electric vehicles,such as golf carts. This type of battery use isalso called Cycle Service.8 Stationary -- Stationary batteries musthave a long shelf life and deliver moderate tohigh currents when called upon. Thesebatteries are most often used for emergencies.Typical uses for stationary batteries are inuninteruptable power supplies (UPS) and foremergency lighting in stairwells and hallways.This type of battery use is also called Standbyor Float.

2.3 “H OUSEHOLD” BATTERIES

“Household” batteries are those batteries thatare primarily used to power small, portabledevices such as flashlights, radios, laptopcomputers, toys, and cellular phones. Thefollowing subsections describe thetechnologies for many of the formerly usedand presently used types of householdbatteries.

Typically, household batteries are small, 1.5 Vcells that can be readily purchased off theshelf. These batteries come in standard shapesand sizes as shown in Table 2. They can alsobe custom designed and molded to fit any sizebattery compartment (e.g., to fit inside acellular phone, camcorder, or laptopcomputer).

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Size Shape and Dimensions Voltage

D Cylindrical, 61.5 mmtall, 34.2 mm diameter.

1.5 V

C Cylindrical, 50.0 mmtall, 26.2 mm diameter.

1.5 V

AA Cylindrical, 50.5 mmtall, 14.5 mm diameter.

1.5 V

AAA Cylindrical, 44.5 mmtall, 10.5 mm diameter

1.5 V

9 Volt Rectangular, 48.5 mmtall, 26.5 mm wide,

17.5 mm deep.

9 V

Note: Three other standard sizes of householdbatteries are available, AAAA, N, and 6-V (lantern)batteries. It is estimated that 90% of portable,battery-operated devices require AA, C, or Dbattery sizes.

Table 2. Various Popular Household-BatterySizes

Zn�2MnO2�2NH4Cl ���

Zn(NH3)2Cl2�2MnOOH

Equation 2. The chemical reaction in aLeclanché cell.

Most of the rest of this guideline will focus ondesigns, features, and uses of householdbatteries.

2.3.1 Zinc-carbon (Z-C)Zinc-carbon cells, also known as “Leclanchécells” are widely used because of theirrelatively low cost. Equation 2 shows thechemical reaction in a Leclanché cell. Theywere the first widely available householdbatteries. Zinc-carbon cells are composed of amanganese dioxide and carbon cathode, a zincanode, and zinc chloride (or ammoniumchloride) as the electrolyte.

Generally, zinc-carbon cells are notrechargeable and they have a slopingdischarge curve (i.e., the voltage leveldecreases relative to the amount of discharge).Zinc-carbon cells will produce 1.5 V, and theyare mostly used for non-critical uses such assmall household devices like flashlights andportable personal radios.

One notable drawback to these kind ofbatteries is that the outer, protective casing ofthe battery is made of zinc. The casing servesas the anode for the cell and, in some cases, ifthe anode does not oxidize evenly, the casingcan develop holes that allow leakage of themildly acidic electrolyte which can damagethe device being powered.

2.3.2 Zinc-Manganese Dioxide AlkalineCells (“Alkaline Batteries”)

When an alkaline electrolyte—instead of themildly acidic electrolyte—is used in a regularzinc-carbon battery, it is called an “alkaline”battery. An alkaline battery can have a usefullife of five to six times that of a zinc-carbonbattery. One manufacturer estimates that 30%of the household batteries sold in the world

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Cd�2H2O�2NiOOH ���

2Ni(OH)2�Cd(OH)2

Equation 3. The chemical reaction in anickel-cadmium battery.

today are zinc-manganese dioxide (i.e.,alkaline) batteries.2,3

2.3.3 Rechargeable Alkaline BatteriesLike zinc-carbon batteries, alkaline batteriesare not generally rechargeable. One majorbattery manufacturer, however, has designed a“reusable alkaline” battery that they market asbeing rechargeable “25 times or more.”4

This manufacturer states that its batteries donot suffer from memory effects as the Ni-Cdbatteries do, and that their batteries have ashelf life that is much longer than Ni-Cdbatteries—almost as long as the shelf life ofprimary alkaline batteries.

Also, the manufacturer states that theirrechargeable alkaline batteries contain notoxic metals, such as mercury or cadmium, tocontribute to the poisoning of theenvironment.

Rechargeable alkaline batteries are mostappropriate for low- and moderate-powerportable equipment, such as hand-held toysand radio receivers.

2.3.4 Nickel-Cadmium (Ni-Cd)Nickel-cadmium cells are the most commonlyused rechargeable household batteries. Theyare useful for powering small appliances, suchas garden tools and cellular phones. The basicgalvanic cell in a Ni-Cd battery contains acadmium anode, a nickel hydroxide cathode,and an alkaline electrolyte. Equation 3 showsthe chemical reaction in a Ni-Cd cell. Batteriesmade from Ni-Cd cells offer high currents atrelatively constant voltage and they aretolerant of physical abuse. Nickel-cadmiumbatteries are also tolerant of inefficient usagecycling. If a Ni-Cd battery has incurredmemory loss (Sec. 3.4), a few cycles ofdischarge and recharge can often restore thebattery to nearly “full” memory.

Unfortunately, nickel-cadmium technology isrelatively expensive. Cadmium is anexpensive metal and is toxic. Recentregulations limiting the disposal of wastecadmium (from cell manufacturing or fromdisposal of used batteries) has contributed tothe higher costs of making and using thesebatteries.

These increased costs do have one unexpectedadvantage. It is more cost effective to recycleand reuse many of the components of a Ni-Cdbattery than it is to recycle components ofother types of batteries. Several of the majorbattery manufacturers are leaders in suchrecycling efforts.

2The Story of Packaged Power, DuracellInternational, Inc., July, 1995.

3Certain commercial companies, equipment,instruments, and materials are identified in this reportto specify adequately the technical aspects of thereported results. In no case does such identificationimply recommendation or endorsement by the NationalInstitute of Justice, or any other U.S. Governmentdepartment or agency, nor does it imply that thematerial or equipment identified is necessarily the bestavailable for the purpose.

4Household Batteries and the Environment,Rayovac Corporation, 1995.

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Lithium will ignite or explode oncontact with water.

2.3.5 Nickel-Metal Hydride (Ni-MH)Battery designers have investigated severalother types of metals that could be usedinstead of cadmium to create high-energysecondary batteries that are compact andinexpensive. The nickel-metal-hydride cell is awidely used alternative.

The anode of a Ni-MH cell is made of ahydrogen storage metal alloy, the cathode ismade of nickel oxide, and the electrolyte is apotassium hydroxide solution.

According to one manufacturer, Ni-MH cellscan last 40% longer than the same size Ni-Cdcells and will have a life-span of up to 600cycles.5 This makes them useful for high-energy devices suchas laptopcomputers, cellularphones, andcamcorders.

Ni-MH batterieshave a high self-discharge rate and arerelatively expensive.

2.3.6 Nickel-Iron (Ni-I)Nickel-iron cells, also known as the Edisonbattery, are much less expensive to build andto dispose of than nickel-cadmium cells.Nickel-iron cells were developed even beforethe nickel-cadmium cells. The cells are ruggedand reliable, but do not recharge veryefficiently. They are widely used in industrialsettings and in eastern Europe, where iron andnickel are readily available and inexpensive.

2.3.7 Nickel-Zinc (Ni-Z)Another alternative to using cadmiumelectrodes is using zinc electrodes. Althoughthe nickel-zinc cell yields promising energyoutput, the cell has some unfortunateperformance limitations that prevent the cellfrom having a useful lifetime of more than 200or so charging cycles. When nickel-zinc cellsare recharged, the zinc does not redeposit inthe same “holes” on the anode that werecreated during discharge. Instead, the zincredeposits in a somewhat random fashion,causing the electrode to become misshapen.Over time, this leads to the physicalweakening and eventual failure of theelectrode.

2.3.8 Lithium andLithium Ion

Lithium is apromising reactantin batterytechnology, due toits high electro-

positivity. The specific energy of somelithium-based cells can be five times greaterthan an equivalent-sized lead-acid cell andthree times greater than alkaline batteries.6

Lithium cells will often have a starting voltageof 3.0 V. These characteristics translate intobatteries that are lighter in weight, have lowerper-use costs, and have higher and more stablevoltage profiles. Equation 4 shows thechemical reaction in one kind of lithium cell.

5The Story of Packaged Power, DuracellInternational, Inc., July, 1995.

6Why Use Energizer AA Lithium Batteries?,Eveready Battery Company, Inc., 1993.

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Li�MnO2 ��� LiMnO2

Equation 4. The chemical reaction in alithium-manganese dioxide cell.

Unfortunately, the same feature that makeslithium attractive for use in batteries—its highelectrochemical potential—also can causeserious difficulties in the manufacture and useof such batteries. Many of the inorganiccomponents of the battery and its casing aredestroyed by the lithium ions and, on contactwith water, lithium will react to createhydrogen which can ignite or can createexcess pressure in the cell. Many fireextinguishers are water based and will causedisastrous results if used on lithium products.Special D-class fire extinguishers must beused when lithium is known to be within theboundaries of a fire.7

Lithium also has a relatively low meltingtemperature for a metal, 180 (C (356 (F). Ifthe lithium melts, it may come into directcontact with the cathode, causing violentchemical reactions.

Because of the potentially violent nature oflithium, the Department of Transportation(DOT) has special guidelines for the transportand handling of lithium batteries. Contactthem to ask for DOT Regulations 49 CFR.

Some manufacturers are having success withlithium-iron sulfide, lithium-manganesedioxide, lithium-carbon monoflouride,lithium-cobalt oxide, and lithium-thionyl cells.

In recognition of the potential hazards oflithium components, manufacturers of lithium-based batteries have taken significant steps toadd safety features to the batteries to ensuretheir safe use.

Lithium primary batteries (in small sizes, forsafety reasons) are currently being marketedfor use in flash cameras and computermemory. Lithium batteries can last three timeslonger than alkaline batteries of the samesize.8 But, since the cost of lithium batteriescan be three times that of alkaline batteries,the cost benefits of using lithium batteries aremarginal.

Button-size lithium batteries are becomingpopular for use in computer memory back-up,in calculators, and in watches. In applicationssuch as these, where changing the battery isdifficult, the longer lifetime of the lithiumbattery makes it a desirable choice.

One company now produces secondarylithium-ion batteries with a voltage of 3.7 V,“four times the energy density of Ni-Cdbatteries,” “one-fifth the weight of Ni-Cdbatteries,” and can be recharged 500 times.9

In general, secondary (rechargeable) lithium-ion batteries have a good high-powerperformance, an excellent shelf life, and abetter life span than Ni-Cd batteries.Unfortunately, they have a very high initial

7Battery Engineering Web Site,http://www.batteryeng.com/, August 1997.

8Navy Primary and Secondary Batteries.Design and Manufacturing Guidelines, NAVSO P-3676, September 1991.

9Battery Engineering Web Site,http://www.batteryeng.com/, August 1997.

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cost and the total energy available per usagecycle is somewhat less than Ni-Cd batteries.

2.4 SPECIALTY BATTERIES (“B UTTON” AND

MINIATURE BATTERIES )

“Button” batteries are the nickname given tothe category of batteries that are small andshaped like a coin or a button. They aretypically used for small devices such ascameras, calculators, and electronic watches.

Miniature batteries are very small batteriesthat can be custom built for devices, such ashearing aids and electronic “bugs,” whereeven button batteries can be too large. Industrystandardization has resulted in five to tenstandard types of miniature batteries that areused throughout the hearing-aid industry.

Together, button batteries and miniaturebatteries are referred to as specialty batteries.

Most button and miniature batteries need avery high energy density to compensate fortheir small size. The high energy density isachieved by the use of highly electro-positive—and expensive—metals such assilver or mercury. These metals are not costeffective enough to be used in larger batteries.

Several compositions of specialty batteries aredescribed in the following sections.

2.4.1 Metal-Air CellsA very practical way to obtain high energydensity in a galvanic cell is to utilize theoxygen in air as a “liquid” cathode. A metal,such as zinc or aluminum, is used as theanode. The oxygen cathode is reduced in aportion of the cell that is physically isolatedfrom the anode. By using a gaseous cathode,

more room is available for the anode andelectrolyte, so the cell size can be very smallwhile providing good energy output. Smallmetal-air cells are available for applicationssuch as hearing aids, watches, and clandestinelistening devices.

Metal-air cells have some technicaldrawbacks, however. It is difficult to build andmaintain a cell where the oxygen acting as thecathode is completely isolated from the anode.Also, since the electrolyte is in direct contactwith air, approximately one to three monthsafter it is activated, the electrolyte will becometoo dry to allow the chemical reaction tocontinue. To prevent premature drying of thecells, a seal is installed on each cell at the timeof manufacture. This seal must be removed bythe customer prior to first use of the cell.Alternately, the manufacturer can provide thebattery in an air-tight package.

2.4.2 Silver OxideSilver oxide cells use silver oxide as thecathode, zinc as the anode, and potassiumhydroxide as the electrolyte. Silver oxide cellshave a moderately high energy density and arelatively flat voltage profile. As a result, theycan be readily used to create specialtybatteries. Silver oxide cells can providehigher currents for longer periods than mostother specialty batteries, such as thosedesigned from metal-air technology. Due tothe high cost of silver, silver oxide technologyis currently limited to use in specialtybatteries.

2.4.3 Mercury OxideMercury oxide cells are constructed with azinc anode, a mercury oxide cathode, andpotassium hydroxide or sodium hydroxide asthe electrolyte. Mercury oxide cells have a

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high energy density and flat voltage profileresembling the energy density and voltageprofile of silver oxide cells. These mercuryoxide cells are also ideal for producingspecialty batteries. The component, mercury,unfortunately, is relatively expensive and itsdisposal creates environmental problems.

2.5 OTHER BATTERIES

This section describes battery technology thatis not mature enough to be available off-the-shelf, has special usage limitations, or isotherwise impractical for general use.

2.5.1 Nickel-Hydrogen (Ni-H)Nickel-hydrogen cells were developed for theU.S. space program. Under certain pressuresand temperatures, hydrogen (which is,surprisingly, classified as an alkali metal) canbe used as an active electrode opposite nickel.Although these cells use an environmentallyattractive technology, the relatively narrowrange of conditions under which they can beused, combined with the unfortunate volatilityof hydrogen, limits the long-range prospects ofthese cells for terrestrial uses.

2.5.2 Thermal BatteriesA thermal battery is a high-temperature,molten-salt primary battery. At ambienttemperatures, the electrolyte is a solid, non-conducting inorganic salt. When power isrequired from the battery, an internalpyrotechnic heat source is ignited to melt thesolid electrolyte, thus allowing electricity to begenerated electrochemically for periods from afew seconds to an hour. Thermal batteries arecompletely inert until the electrolyte is meltedand, therefore, have an excellent shelf life,require no maintenance, and can tolerate

physical abuse (such as vibrations or shocks)between uses.

Thermal batteries can generate voltages of 1.5 V to 3.3 V, depending on the battery’scomposition. Due to their rugged constructionand absence of maintenance requirements,they are most often used for militaryapplications such as missiles, torpedoes, andspace missions and for emergency-powersituations such as those in aircraft orsubmarines.

The high operating temperatures and shortactive lives of thermal batteries limit their useto military and other large-institutionapplications.

2.5.3 Super CapacitorThis kind of battery uses no chemical reactionat all. Instead, a special kind of carbon (carbonaerogel), with a large molecular surface area,is used to create a capacitor that can hold alarge amount of electrostatic energy.10 Thisenergy can be released very quickly, providinga specific energy of up to 4000 Watt-hours perkilogram (Wh/kg), or it can be regulated toprovide smaller currents typical of manycommercial devices such as flashlights, radios,and toys. Because there are no chemicalreactions, the battery can be rechargedhundreds of thousands of times withoutdegradation. Other potential advantages of thiskind of cell are its low cost and widetemperature range. One disadvantage,however, is its high self-discharge rate. Thevoltage of some prototypes is approximately2.5 V.

10PolyStor Web Page, http://www.polystor.com/, August, 1997.

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2.5.4 The Potato BatteryOne interesting science experiment involvessticking finger-length pieces of copper andzinc wire, one at a time, into a raw potato tocreate a battery. The wires will carry a veryweak current which can be used to power asmall electrical device such as a digital clock.

One vendor sells a novelty digital watch that ispowered by a potato battery. The wearer mustput a fresh slice of potato in the watch everyfew days.

2.5.5 The Sea BatteryAnother interesting battery design uses a rigidframework, containing the anode and cathode,which is immersed into the ocean to use seawater as the electrolyte. This configurationseems promising as an emergency battery formarine use.

2.5.6 Other DevelopmentsScientists are continually working on newcombinations of materials for use in batteries,as well as new manufacturing methods toextract more energy from existingconfigurations.

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Figure 2. Energy densities, W#h/kg, of variousbattery types (adapted from NAVSO P-3676).

3. Performance, Economics and Tradeoffs

3.1 ENERGY DENSITIES

The energy density of a battery is a measure ofhow much energy the battery can supplyrelative to its weight or volume. A battery withan energy density twice that of another batteryshould, theoretically, have an active lifetimetwice as long.

The energy density of a battery is mainlydependent on the composition of its activecomponents. A chemist can use mathematicalequations to determine the theoreticalmaximum voltage and current of a proposedcell, if the chemical composition of the anode,cathode, and electrolyte of the cell are allknown. Various physical attributes, such aspurity of the reactants and the particulars ofthe manufacturing process can cause themeasured voltage, current, and capacity to belower than their theoretical values.

3.2 ENERGY PER MASS

Figure 2 compares the gravimetric energydensities of various dry cell systemsdischarged at a constant rate for temperatures between -40 (C (-40 (F) and 60 (C (140 (F).

Of the systems shown, the zinc-air cellproduces the highest gravimetric energydensity. Basic zinc-carbon cells have thelowest gravimetric energy density.

3.3 ENERGY PER VOLUME

Figure 3 compares the volumetric energydensities of various dry cell systemsdischarged at a constant rate for temperaturesbetween -40 (C (-40 (F) and 60 (C (140 (F).

Of the systems shown, the zinc-air cellproduces the highest volumetric energydensity. Basic zinc-carbon cells have thelowest volumetric energy density. The curvesfor secondary battery cells are not shown inthe tables.

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Figure 3. Energy densities, W#h/L, of variousbattery types (adapted from NAVSO P-3676).

Of the major types of secondary cells, Ni-Cdbatteries and wet-cell lead-acid batteries haveapproximately the same volumetric energydensity. Ni-MH batteries have approximatelytwice the volumetric energy density of Ni-Cdbatteries.

3.4 MEMORY EFFECTS

As a rechargeable battery is used, recharged,and used again, it loses a small amount of itsoverall capacity. This loss is to be expected inall secondary batteries as the active compo-nents become irreversibly consumed.

Ni-Cd batteries, however, suffer an additionalproblem, called the memory effect. If a Ni-Cdbattery is only partially discharged beforerecharging it, and this happens several times ina row, the amount of energy available for thenext cycle will only be slightly greater than theamount of energy discharged in the cell’smost-recent cycle. This characteristic makes itappear as if the battery is “remembering” how

much energy is needed for a repeatedapplication.

The physical process that causes the memoryeffect is the formation of potassium-hydroxidecrystals inside the cells. This build up ofcrystals interferes with the chemical process ofgenerating electrons during the next battery-use cycle. These crystals can form as a resultof repeated partial discharge or as a result ofovercharging the Ni-Cd battery.

The build up of potassium-hydroxide crystalscan be reduced by periodically reconditioningthe battery. Reconditioning of a Ni-Cd batteryis accomplished by carefully controlled powercycling (i.e., deeply discharging and thenrecharging the battery several times). Thispower cycling will cause most of the crystalsto redissolve back into the electrolyte. Severalcompanies offer this reconditioning service,although battery users can purchase areconditioner and recondition their ownbatteries. Some batteries can be reconditionedwithout a special reconditioner by completelydraining the battery (using the battery powereddevice itself or a resistive circuit designed tosafely discharge the battery) and charging it asnormal.

3.5 VOLTAGE PROFILES

The voltage profile of a battery is the relation-ship of its voltage to the length of time it hasbeen discharging (or charging). In mostprimary batteries, the voltage will dropsteadily as the chemical reactions in the cellare diminished. This diminution leads to analmost-linear drop in voltage, called a slopingprofile. Batteries with sloping voltage profilesprovide power that is adequate for many

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Figure 4. Flat discharge curve vs. slopingdischarge curve.

applications such as flashlights, flash cameras,and portable radios.

Ni-Cd batteries provide a relatively flatvoltage profile. The cell’s voltage will remainrelatively constant for more than E of itsdischarge cycle. At some point near the end ofthe cycle, the voltage drops sharply to nearlyzero volts. Batteries with this kind of profileare used for devices that require a relativelysteady operating voltage.

One disadvantage of using batteries with a flatvoltage profile is that the batteries will need tobe replaced almost immediately after a drop involtage is noticed. If they are not immediatelyreplaced, the batteries will quickly cease toprovide any useful energy.

Figure 4 shows the conceptual differencebetween a flat discharge rate and a slopingdischarge rate.

Figure 5 (Sec. 5) shows actual voltageprofiles for several common battery types.

3.6 SELF-DISCHARGE RATES

All charged batteries (except thermal batteriesand other batteries specifically designed for anear-infinite shelf life) will slowly lose theircharge over time, even if they are notconnected to a device. Moisture in the air andthe slight conductivity of the battery housingwill serve as a path for electrons to travel tothe cathode, discharging the battery. The rateat which a battery loses power in this way iscalled the self-discharge rate.

Ni-Cd batteries have a self-discharge rate ofapproximately 1% per day. Ni-MH batterieshave a much higher self-discharge rate ofapproximately 2% to 3% per day. These highdischarge rates require that any such battery,which has been stored for more than a month,be charged before use.

Primary and secondary alkaline batteries havea self-discharge rate of approximately 5% to10% per year, meaning that such batteries canhave a useful shelf life of several years.Lithium batteries have a self-discharge rate ofapproximately 5% per month.

3.7 OPERATING TEMPERATURES

As a general rule, battery performancedeteriorates gradually with a rise intemperature above 25 (C (77 (F), andperformance deteriorates rapidly attemperatures above 55 (C (131 (F). At verylow temperatures -20 (C (-4 (F) to 0 (C (32 (F), battery performance is only a fractionof that at 25 (C (77 (F). Figure 2 and Figure3 show the differences in energy density as afunction of temperature.

At low temperatures, the loss of energycapacity is due to the reduced rate of chemical

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reactions and the increased internal resistanceof the electrolyte. At high temperatures, theloss of energy capacity is due to the increaseof unwanted, parasitic chemical reactions inthe electrolyte.

Ni-Cd batteries have a recommendedtemperature range of +17 (C (62 (F) to 37 (C(98 (F). Ni-MH have a recommendedtemperature range of 0 (C (32 (F) to 32 (C(89 (F).

3.8 CYCLE L IFE

The cycle life of a battery is the number ofdischarge/recharge cycles the battery cansustain, with normal care and usage patterns,before it can no longer hold a useful amountof charge.

Ni-Cd batteries should have a normal cyclelife of 600 to 900 recharge cycles. Ni-MHbatteries will have a cycle life of only 300 to400 recharge cycles. As with all rechargeablebatteries, overcharging a Ni-Cd or Ni-MHbattery will significantly reduce the number ofcycles it can sustain.

3.9 CAPACITY TESTING

Many battery manufacturers recommend theconstant-load test to determine the capacity ofa battery. This test is conducted by connectinga predetermined load to the battery and thenrecording the amount of time needed todischarge the battery to a predetermined level.

Another recommended test is the intermittent-or switching-load test. In this type of test, apredetermined load is applied to the battery fora specified period and then removed foranother period. This load application andremoval is repeated until the battery reaches a

predetermined level of discharge. This kind of test simulates the battery usage of a portableradio.

A comparison of these two kinds of tests wasperformed on five commonly available typesof batteries.11 The data shows that the fivetested batteries all had a constant-loadduration of 60 to 80 minutes, which indicatesthat the five batteries had similar capacities.

But, intermittent-load testing of those samefive batteries showed that the duration of thebatteries ranged from 8.5 hours to 12 hours. There was no correlation of the results of thetwo tests, meaning that batteries thatperformed best under constant-load testing didnot necessarily perform well underintermittent-load testing. The study concludedthat the ability of a battery to recover itselfbetween heavy current drains cannot be madeapparent through a constant-load test.

3.10 BATTERY TECHNOLOGY COMPARISON

Table 3 shows a comparison of some of theperformance factors of several commonbattery types.

The initial capacity of a battery refers to theelectrical output, expressed in ampere-hours,which the fresh, fully charged battery candeliver to a specified load. The rated capacityis a designation of the total electrical output ofthe battery at typical discharge rates; e.g., foreach minute of radio transceiver operation, 6seconds shall be under a transmit current

11Batteries Used with Law EnforcementCommunications Equipment: Chargers and ChargingTechniques, W. W. Scott, Jr., U.S. Department ofJustice, LESP-RPT-0202.00, June 1973.

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(See Sec. 3.10) Ni-Cd Ni-MH PrimaryAlkaline

SecondaryAlkaline

Initial Capacity r || NNNN qqq

Rated Capacity NNNN qqq || r

Self-Discharge || r NNNN NNNN

Cycle Life NNNN NNNN r qqq

Initial Cost* || r NNNN qqq

Life-Cycle Cost* qqq qqq r qqq

Worst Performance = r, Low Performance = ||,Good Performance= qqq, Best Performance =NNNN*A better performance ranking means lower costs.

Table 3. Battery Technology Comparison (adapted fromDesign Note: Renewable Reusable Alkaline Batteries)

drain, 6 seconds shall be under a receivecurrent drain and 48 seconds shall be under astandby current drain.

The self-discharge rate is the rate at which thebattery will lose its charge during storage orother periods of non-use. The cycle life is thenumber of times that the rechargeable batterycan be charged and discharged before itbecomes no longer able to hold or deliver anyuseful amount of energy.

The initial cost is the relative cost ofpurchasing the battery. The life-cycle cost isthe per-use relative cost of the battery.

Table 4 shows a more detailed comparison ofmany of the available battery types.

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Cell Type* BasicType**

Anodematerial

CathodeMaterial

MainElectrolyteMaterial

VoltsperCell

Advantages &Applications

Disadvantages

Carbon-Zinc(“Leclanché”)

P Zinc Manganesedioxide

Ammoniumchloride, zinc

chloride

1.5 Low cost, good shelflife. Useful forflashlights, toys, andsmall appliances.

Output capacitydecreases as itdrains; poorperformance atlow temperatures.

Zinc Chloride P Zinc Manganesedioxide

Zinc Chloride 1.5 Good service at highdrain, leak resistant,good low-temperatureperformance. Useful forflashlights, toys, andsmall appliances.

Relativelyexpensive fornovelty usage.

“Alkaline”(Zinc-

ManganeseDioxide)

P or S Zinc Manganesedioxide

Potassiumhydroxide

1.5 High efficiency undermoderate, continuousdrains, long shelf life,good low-temperatureperformance. Useful forcamera flash units,motor-driven devices,portable radios.

Primary cells areexpensive fornovelty usage.Secondary cellshave a limitednumber ofrecharge cycles.

Car Battery(Lead-Acid)

S Lead Lead dioxide Sulfuric acid 2 Low cost, spill resistant(sealed batteries). Usefulfor automobiles andcordless electric lawnmowers.

Limited low-temperatureperformance.Vented cellsrequiremaintenance.Cells are relativelyheavy.

* -- Common name, ** -- P=Primary, S=Secondary (Rechargeable)

Table 4. A Comparison of Several Popular Battery Types

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Cell Type* BasicType**

Anodematerial

CathodeMaterial

MainElectrolyteMaterial

VoltsperCell

Advantages &Applications

Disadvantages

“Ni-Cd” (Nickel-Cadmium)

S Cadmium Nickelhydroxide

Potassiumhydroxide

1.25 Excellent cycle life; flatdischarge curve; goodhigh- and low-temperatureperformance; highresistance to shock andvibration. Useful forsmall appliances thathave intermittent usage,such as walkie-talkies,portable hand tools, tapeplayers, and toys. Whenbatteries are exhausted,they can be rechargedbefore the next neededuse.

High initial cost;only fair chargeretention;memory effect.

Mercuric Oxide P Zinc Mercuricoxide

Potassiumhydroxide

1.35 Relatively flat dischargecurve; relatively highenergy density; goodhigh-temperatureperformance; goodservice maintenance.Useful for criticalappliances, such aspaging, hearing aids, andtest equipment.

Poor low-temperatureperformance insome situations.

* -- Common name, ** -- P=Primary, S=Secondary (Rechargeable)

Table 4 (continued)

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Cell Type* BasicType**

Anodematerial

CathodeMaterial

MainElectrolyteMaterial

VoltsperCell

Advantages &Applications

Disadvantages

“Ni-MH”(Nickel-Metal

Hydride)

S Hydrogenstorage metal

Nickel oxide Potassiumhydroxide

1.5 No memory effects (suchas Ni-Cd has), goodhigh-powerperformance, good low-temperatureperformance. Useful forportable devices wherethe duty cycle variesfrom use to use.

High initial cost,relatively highrate of self-discharge.

Silver Oxide P or S Zinc Silver oxide Potassiumhydroxide

1.5 High energy density; flatdischarge curve. Usefulfor very small appliancessuch as calculators,watches, and hearingaids.

Silver is veryexpensive; poorstorage andmaintenancecharacteristics.Rechargeablecells have a verylimited number ofcycles.

Zinc-Air P Zinc Oxygen Potassiumhydroxide

1.25 High energy density insmall cells. Flatdischarge rate.

Dries out quickly.

Lithium P Lithium Iron sulfide Lithium saltsin ether

1.0 -3.6

Good energy density. Limited high-ratecapacities; safetyconcerns.

* -- Common name, ** -- P=Primary, S=Secondary (Rechargeable)

Table 4 (continued)

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Figure 5. Performance comparison of primary andsecondary alkaline and Ni-Cd batteries (adapted fromDesign Note: Renewable Reusable Alkaline Batteries).

4. Selecting the Right Battery for theApplication

Batteries come in many different shapes, sizes,and compositions. There is no one “ideal”battery that can satisfy all possiblerequirements equally. Different batterytechnologies have been developed that willoptimize certain parameters for specificbattery uses.

In general, theenergy outputof a battery isrelated only toits size andmaterialcomposition.Differentbattery designsand differentmanufacturingmethods (forthe same type,size, andcomposition ofbattery) will, ingeneral, lead toonly minordifferences inthe batteries’ electrical output. Battery-industry standards have contributed to the factthat batteries (of the same type, composition,and size) from different manufacturers arequite interchangeable.

However, the small differences that do existbetween batteries made by differentmanufacturers, can be significant when using amulti-cell array of matched cells. In thesecases, potential replacement cells must begraded to see if the cells properly match thecapacity of the existing cells.

Even for non-matched, multi-cellapplications,such asflashlights,portable radios,etc., it is still agood rule ofthumb to avoidmixing batteriesfrom differentmanufacturerswithin onedevice. Smallvariances involtage andcurrent,between

different brands of battery, can slightly shortenthe useful life span of all of the batteries.

Do not mix batteries of different types (e.g.,do not mix rechargeable alkaline batteries withNi-Cd batteries) within a single device orwithin an array of batteries.

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Figure 5 shows some discharge curves forseveral popular AA size battery types. Two ofthe curves (secondary alkaline [1st use] and[25th use]) show that secondary alkalinebatteries rapidly lose their capacity as they areused and recharged. Only one Ni-Cd curve isshown, since its curve remains essentially thesame throughout most its life span.

4.1 BATTERY PROPERTIES

Battery applications vary, as do considerationsfor selecting the correct battery for eachapplication. Some of the important factors thatcustomers might consider when selecting theright battery for a particular application arelisted below:

Chemistry -- Which kind ofbattery chemistry is best for the application?Different chemistries will generate differentvoltages and currents.

Primary or Secondary -- Primarybatteries are most appropriate for applicationswhere infrequent, high-energy output isrequired. Secondary batteries are mostappropriate for use in devices that see steadyperiods of use and non-use (pagers, cellularphones, etc.).

Standardization andAvailability -- Is there an existing batterydesign that meets the application needs? Willreplacement batteries be available in thefuture? Using existing battery types is almostalways preferable to specifying a custom-madebattery design.

Flexibility -- Can the batteryprovide high or low currents over a wide rangeof conditions?

Temperature Range -- Can thebattery provide adequate power over the

expected temperature range for theapplication?

Good Cycle Life -- How manytimes can the rechargeable battery bedischarged and recharged before it becomesunusable?

Costs -- How expensive is thebattery to purchase? Does the battery requirespecial handling?

Shelf Life -- How long can thebattery be stored without loss of a significantamount of its power?

Voltage -- What is the voltage ofthe battery? [Most galvanic cells producevoltages of between 1.0 and 2.0 V.]

Safety -- Battery componentsrange from inert, to mildly corrosive, to highlytoxic or flammable. The more hazardouscomponents will require additional safetyprocedures.

Hidden Costs -- Simplermanufacturing processes result in lower costbatteries. However, if a battery contains toxicor hazardous components, extra costs will beincurred to dispose of the battery safely afterits use.

Table 5 shows a short list of different batterytypes and the kinds of application that areappropriate for each.

4.2 ENVIRONMENTAL CONCERNS

All battery components, when discarded,contribute to the pollution of the environment.Some of the components, such as paperboardand carbon powder, are relatively organic andcan quickly merge into the ecosystem withoutnoticeable impact. Other components, such assteel, nickel, and plastics, while not actively

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BatteryType

DeviceDrain Rate

Device UseFrequency

PrimaryAlkaline

High Moderate

SecondaryAlkaline

Moderate Moderate

PrimaryLithium

High Frequent

SecondaryNi-Cd

High Frequent

Primary Zn-C(“HeavyDuty”)

Moderate Regular

Primary Zn-C(“Standard”)

Low Occasional

Table 5. Recommended Battery Types forVarious Usage Conditions

Many of the major battery manufacturershave put significant efforts into therecycling of discarded batteries.

toxic to the ecosystem, will add to the volumeof a landfill, since they decompose slowly.

Of most concern,however, are theheavy-metal batterycomponents,which, whendiscarded, can betoxic to plants,animals, andhumans. Cadmium, lead, and mercury are theheavy-metal components most likely to be thetarget of environmental concerns.

Several of the major battery manufacturershave taken steps to reduce the amount of toxicmaterials in their batteries. One manufacturerreports the reduction of the mercury content oftheir most-popular battery from 0.75%, in

1980, to 0.00%, in 1996.12 Othermanufacturers report that their current batteryformulas contain no mercury. The U.S.Department of Mines, in 1994, estimated that,for the U.S. production of household batteries,mercury usage had fallen from 778 tons in1984 to (a projected) 10 tons in 1995.13

Many of the major battery manufacturers haveput significant efforts into the recycling ofdiscarded batteries. According to onemanufacturer, it takes six to ten times moreenergy to recycle a battery than to create thebattery components from virgin materials.Efforts are underway that could improve therecycling technology to make recyclingbatteries much more energy efficient and costeffective.14

The use of secondary (rechargeable) batteriesis more cost efficient than the use of primarybatteries. Such use will reduce the physicalvolume of discarded batteries in landfills,because the batteries can be recharged andreused 25 to 1000 times before they must be

discarded.

12Eveready and the Environment, EvereadyBattery Company, Inc., 1995.

13Eveready and the Environment, EvereadyBattery Company, Inc., 1995.

14Eveready and the Environment, EvereadyBattery Company, Inc., 1995.

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The most popular secondary batteries,however, contain cadmium. Manymanufacturers, responding to customerrequests and legislative demands, aredesigning nickel-metal hydride, lithium-ion,and rechargeable-alkaline secondary batteriesthat contain only trace amounts of cadmium,lead, or mercury.

4.3 STANDARDIZATION

Existing off-the-shelf batteries are oftenpreferred to batteries that require specialdesign and manufacturing. Some benefits ofusing off-the-shelf batteries are listed below:

The use of a proven design canreduce the risk of the battery not workingproperly.

The use of tested technologyeliminates costly and time-consumingdevelopment efforts.

The use of a proven design reducesunit production costs because of competitive,multi-source availability.

The use of tested technologyreduces operations and support costs throughcommonality of training, documentation, andreplacement efforts.

4.4 TESTING CAPACITIES

One method of estimating battery capacityrequirements for a specific battery-powereddevice is to calculate the current drawn duringthe typical duty cycle for the device.

Standard duty cycles for battery service lifeand capacity determinations are defined inEIA/TIA Standard 60315 for land mobile radiocommunications and NIJ Standard-0211.0116

for hand-held portable radio applications.Specifically, in an average 1 minute period ofmobile-radio usage, 6 seconds (10%) is spentreceiving, 6 seconds (10%) is spenttransmitting and 48 seconds (80%) is spent inthe idle mode. Table 8 provides an exampleof a transceiver drawing an average current of8.0 + 6.2 + 32.5 = 46.7 mA. For a typical dutycycle composed of 8 hours of operation(followed by 16 hours of rest) a minimumbattery capacity of 374 mAh is required. Onemanufacturer of portable communicationsequipment recommends that batteries bereplaced if they fail to deliver 80% or more oftheir original rated capacity. Below 80%batteries are usually found to deterioriatequickly. Because a minimum requirement of374 mAh is 75% of the rated capacity of a 500mAh battery, the latter should adequatelyprovide power for the entire duty described.17

15Land Mobile FM or PM CommunicationsEquipment, Measurement and Performance Standard,Electronics Industry Association/TelecommunicationsIndustry Association, Publication EIA/TIA 603, 1993.

16Rechargeable Batteries for Personal/Portable Transceivers, National Institute of Justice,NIJ Standard-0211.01, 1995.

17Batteries Used with Law EnforcementCommunications Equipment: Chargers and ChargingTechniques, W.W. Scott, Jr., National Institute ofJustice, LESP-RPT-0202.00, June 1973.

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StandbyMode

ReceiveMode

TransmitMode

Percent ofDuty Cycle

80%(48 minutes

of eachhour)

10%(6 minutes

of eachhour)

10%(6 minutes ofeach hour)

CurrentDrain for Mode

10 mA 62 mA 325 mA

AverageCurrent forMode

8.0 mA 6.2 mA 32.5 mA

Table 6. Typical Usage of PortableTelecommunications Equipment.

Similar calculations can be performed for anybattery in any battery-powered device by usingthe data relevant to the device and theproposed battery. The manufacturers shouldeither provide such appropriate informationwith the batteries and devices, or they shouldbe able to provide those data on request.

4.5 MOBILE RADIOS

As reported above, mobile radios have atypical duty cycle of 10% transmit, 10%receive, and 80% standby. The maximumcurrent drain will occur during the transmitcycle. Each radio, typically, will have a dailycycle of 8 hours of use and 16 hours of non-use. The non-use hours may be used to chargethe radio’s batteries.

Most commercial, off-the-shelf mobile-radiounits include a battery. But, since many radiounits are in service 7 days a week, 52 weeks ayear, and since the batteries are discharged andrecharged daily, each set of batteries shouldwear out approximately once every two years(~700 recharge cycles). Replacement batteries

should be purchased as directed by the usermanual for the unit.

4.6 CELLULAR PHONES AND PCS PHONES

Most commercial, off-the-shelf cellularphones contain a battery when purchased. Charging units may be supplied with thephone or may be purchased separately.

Typical usage for cellular telephones will varysignificantly with user, but, the estimate formobile radio usage (10% of the duty cycle isspent in transmit mode, 10% in receive mode,and 80% in standby mode) is also a reasonableestimate for cellular phone usage. At the endof each usage cycle, the user places the battery(phone) on a recharging unit that will chargethe battery for the next usage cycle. This usagepattern is appropriate for Ni-Cd or Ni-MHbatteries. Ni-Cd batteries should becompletely discharged between uses toprevent memory effects created by a recurringduty cycle.

When a replacement or spare battery isneeded, only replacements, recommended bythe phone manufacturer should be used.

Batteries and battery systems from othermanufacturers may be used if the batteries arecertified to work with that particular brand andmodel of phone. Damage to the phone mayresult if non-certified batteries are used.

Several battery manufacturers makereplacement battery packs that are designed towork with a wide variety of cellular phones. Because of the variety of phones available,battery manufacturers must design and sellseveral dozen different types of batteries to fitthe hundreds of models of cellular phones

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from dozens of different manufacturers.18 Theuser is advised to check battery inter-operability charts before purchasing areplacement battery.

One battery manufacturer offers a batteryreplacement system that allows a phone ownerto use household primary batteries, insertedinto a special housing (called a refillablebattery pack), to replace the phone’s regularrechargeable battery pack. This refillable pack,says the manufacturer, is designed for light-use customers, who require that their phone’sbatteries have the long shelf life of primarybatteries. This refillable pack can also be usedin emergencies, for example, where thephone’s rechargeable battery pack isexhausted and no recharged packs areavailable. Primary household batteries can bereadily purchased (or borrowed from otherdevices), inserted into the refillable pack, andused to power the phone.19

4.7 LAPTOP COMPUTERS

Most commercial, off-the-shelf laptopcomputers have a built-in battery system. Inaddition to the battery provided, most laptopswill have a battery adapter that also serves as abattery charger.

The expected usage of a laptop computer isthat the operator will use it several times aweek, for periods of several hours at a time. The computer will drain the battery at amoderate rate when the computer is running,

and at the self-discharge rate when thecomputer is shut off. Quite often, the user willuse the computer until the “low battery” alarmsounds. At this point, the battery will bedrained of 90% of its charge before the userrecharges it. The computer will also registerregular periods of non-use, during which thebattery can be recharged. Secondary Ni-Cdbatteries are most appropriate for this usagepattern.

When a laptop-computer battery reaches theend of its life cycle, it should be replaced witha battery designed specifically for that laptopcomputer. Using other types of batteries maydamage the computer. The user’s manual forthe laptop computer will list one or morebattery types and brands that may be used. Ifin doubt, the user is advised to contact themanufacturer of the laptop computer and askfor a battery-replacement recommendation.

4.8 CAMCORDERS

Almost all commercial, off-the-shelfcamcorders come with a battery and arecharging unit when purchased.

The camcorder is typically operatedcontinuously for several minutes or hours (toproduce a video recording of some event).This use will require that the battery provideapproximately 2 hours of non-stop recordingtime. The electric motor driving the recordingtape through the camcorder requires amoderately high amount of power throughoutthe entire recording period.

Rechargeable Ni-Cd or Ni-MH batteries orprimary lithium batteries are usually the onlychoice for camcorder use. Several batterymanufacturers produce Ni-Cd or Ni-MH

18Easy to Choose, Easy to Use, EvereadyBattery Corporation, 1997.

19Cellular Duracell Rechargeable Batteries,Duracell, 1996.

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batteries that are specially designed for use incamcorders. Due to the lack of sufficientstandardization for these kind of batteries, thebattery manufacturers must design and sellapproximately 20 different camcorderbatteries to fit at least 100 models ofcamcorders from over a dozenmanufacturers.20

Camcorder batteries are usually designed toprovide 2 hours of service, but larger batteriesare available that can provide up to 4 hours ofservice.

Lithium camcorder batteries can provide three to five times the energy of a single cycle ofsecondary Ni-Cd batteries. These lithiumbatteries, however, are primary batteries andmust be properly disposed of at the end oftheir life cycle. Secondary lithium-ioncamcorder batteries are being developed.

4.9 SUMMARY

There are six varieties of batteries in use, eachwith its own advantages and disadvantages.Below is a short summary of each variety:

_ Lead-Acid -- Secondary lead-acidbatteries are the most popular worldwide.Both the battery product and themanufacturing process are proven,economical, and reliable._ Nickel-Cadmium -- Secondary Ni-Cdbatteries are rugged and reliable. They exhibita high-power capability, a wide operatingtemperature range, and a long cycle life. Theyhave a self-discharge rate of approximately1% per day.

_ Alkaline -- The most commonly usedprimary cell (household) is the zinc-alkalinemanganese dioxide battery. They providemore power-per-use than secondary batteriesand have an excellent shelf life._ Rechargeable Alkaline -- Secondaryalkaline batteries have a long shelf life and areuseful for moderate-power applications. Theircycle life is less than most other secondarybatteries._ Lithium Cells -- Lithium batteries offerperformance advantages well beyond thecapabilities of conventional aqueouselectrolyte battery systems. However, lithiumbatteries are not widely used because of safetyconcerns._ Thermal Batteries -- These are specialbatteries that are capable of providing veryhigh rates of discharge for short periods oftime. They have an extremely long shelf life,but, because of the molten electrolyte and highoperating temperature, are impractical formost household uses.

20Camcorder Battery Pocket Guide, EvereadyBattery Company, 1996.

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5. Battery Handling and Maintenance

The following guidelines offer specific adviceon battery handling and maintenance. Thisadvice is necessarily not all inclusive. Usersare cautioned to observe specific warnings onindividual battery labels and to use commonsense when handling batteries.

5.1 BATTERY DANGERS

8 To get help, should someone swallow abattery, immediately call The NationalBattery Ingestion Hot Line collect at(202) 625-3333. Or, call 911 or astate/local Poison Control Center.

8 Batteries made from lead (or other heavymetals) can be very large and heavyand can cause damage to equipment orinjuries to personnel if improperlyhandled.

8 When using lithium batteries, a “Lith-X”or D-Class fire extinguisher shouldalways be available. Water-basedextinguishers must not be used onlithium of any kind, since water willreact with lithium and release largeamounts of explosive hydrogen.

� Before abusively testing a battery, contactthe manufacturer of the battery toidentify any potential dangers.

8 Vented batteries must be properlyventilated. Inadequate ventilation mayresult in the build up of volatile gases,

which may result in an explosion orasphyxiation.

� Do not attempt to solder directly onto aterminal of the battery. Attempting todo so can damage the seal or the safetyvent.

� When disconnecting a battery from thedevice it is powering, disconnect oneterminal at a time. If possible, firstremove the ground strap at itsconnection with the device’sframework. Observing this sequencecan prevent an accidental short circuitand also avoid risking a spark at thebattery. In most late-model, domesticautomobiles, the battery terminallabeled “negative” is usually connectedto the automobile’s framework.

� Do not attempt to recharge primarybatteries. This kind of battery is notdesigned to be recharged and mayoverheat or leak if recharging isattempted.

8 When recharging secondary batteries, use acharging device that is approved forthat type of battery. Using an approvedcharging device can preventovercharging or overheating thebattery. Many chargers have specialcircuits built into them for correctlycharging specific types of batteries and

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will not work properly with othertypes.

� Do not use secondary (rechargeable)batteries in smoke detectors.Secondary batteries have a high self-discharge rate. Primary batteries have amuch longer shelf life and are muchmore dependable in emergencies.Consult the smoke detector’s usermanual for the recommended batterytypes.

� Do not attempt to refill or repair a worn-outor damaged battery.

� Do not allow direct bodily contact withbattery components. Acidic or alkalineelectrolyte can cause skin irritation orburns. Electrode materials such asmercury or cadmium are toxic.Lithium can cause an explosion if itcomes into contact with water. Othercomponents can cause a variety ofshort-term (irritation and burns) orlong-term (nerve damage) maladies.

� Do not lick a 9 V battery to see if it ischarged. You will, of course, be able todetermine whether or not the battery ischarged, but such a test may result in aburn that may range from simplyuncomfortable to serious.

� Do not dispose of batteries in a fire. Themetallic components of the battery willnot burn and the burning electrolytemay splatter, explode, or release toxicfumes. Batteries may be disposed of,however, in industrial incinerators thatare approved for the disposal ofbatteries.

� Do not carry batteries in your pocket. Coins, keys, or other metal objects canshort circuit a battery, which can causeextreme heat, acid leakage, or anexplosion.

� Do not wear rings, metal jewelry, or metalwatchbands while handling chargedcells. Severe burns can result fromaccidentally short circuiting a chargedcell. Wearing gloves can reduce thisdanger.

� Do not use uninsulated tools near chargedcells. Do not place charged cells onmetal workbenches. Severe arcing andoverheating can result if the battery’sterminals are shorted by contact withsuch metal objects.

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The Straight Dopeby Cecil Adams, The Chicago Reader

Is it true that refrigerating batteries willextend shelf life? If so, why does a cold carbattery cause slower starts? The answerwill help me sleep better. — Kevin C.,Alexandria, Virginia

Whatever it takes, dude. Refrigeratingbatteries extends shelf life because batteriesproduce electricity through a chemicalreaction. Heat speeds up any reaction, whilecold slows it down. Freeze your [carbattery] and you’ll extend its life becausethe juice won’t leak away—but it’ll alsomake those volts a little tough to use rightaway. That accounts for the beliefoccasionally voiced by mechanics that if abattery is left on the garage floor for anextended period, the concrete will “suckout the electricity.” It does nothing of thekind, but a cold floor will substantiallyreduce a battery’s output. The cure: warmit up first.

(Reprinted, with permission, from Return of the Straight Dope.©1994 Chicago Reader, Inc.)

5.2 EXTENDING BATTERY L IFE

8 Read the instructions for the device beforeinstalling batteries. Be sure to orientthe battery’s positive and negativeterminals correctly when insertingthem.

8 In a device, use only the type of batterythat is recommended by themanufacturer of the device.

8 To find a replacement battery that workswith a given device, call themanufacturer of the device or ask theretailer to check the manufacturer’sbattery cross-reference guide.

8 Store batteries in a cool, dark place. Thishelps extend their shelf life.Refrigerators are convenient locations.Although some battery manufacturerssay that refrigeration has no positiveeffect on battery life, they say it has nonegative effect either. Do not storebatteries in a freezer. Always letbatteries come to room temperaturebefore using them.

8 Store batteries in their original boxes orpackaging materials. The batterymanufacturer has designed thepackaging for maximum shelf life.

8 When storing batteries, remove any load orshort circuit from their terminals.

8 When storing battery-powered devices forlong periods (i.e., more than a month),remove the batteries. This can preventdamage to the device from possiblebattery leakage. Also, the batteries canbe used for other applications while thebatteries are still “fresh.”

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8 Use a marking pen to indicate, on thebattery casing, the day and year that thebattery was purchased. Also, keeptrack of the number of times thebattery has been recharged. Avoidwriting on or near the batteryterminals.

8 Do not mix batteries from differentmanufacturers in a multi-cell device(e.g., a flashlight). Small differences involtage, current, and capacity, betweenbrands, can reduce the average usefullife of all the batteries.

8 When using secondary batteries in a multi-cell device (e.g., a flashlight), try touse batteries of the same age andsimilar charging histories. This kind ofmatching will make it more likely thatall the batteries will discharge at thesame rate, putting less stress on anyindividual battery.

8 When using single-cell rechargeable Ni-Cdbatteries, be sure to discharge the cellcompletely before recharging it, thuscounteracting the “memory” effect.

8 Secondary Ni-Cd batteries can sometimesbe reconditioned to reduce the impactof “memory” effects. Completelydischarge the battery and recharge itseveral times.

� Do not use batteries in high-temperaturesituations (unless the battery isdesigned for that temperature range).Locate batteries as far away from heatsources as possible. The electricalpotential of the battery will degraderapidly if it is exposed to temperatures

higher than those recommended by themanufacturer.

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Description Charge Rate(Amperes)

Nominal ChargeTime (Hours)

Standby(Trickle)

0.01 C to 0.03 C 100 to 33

Slow(Overnight)

0.05 C to 0.1 C 20 to 10

Quick 0.2 C to 0.5 C 5 to 2

Fast 1 C and more 1 and less

“C” is the theoretical current needed to completelycharge the fully discharged battery in one hour.

Table 7. Charge Rate Descriptions

6. Battery Chargers and Adapters

6.1 BATTERY CHARGERS

Secondary (rechargeable) batteries require abattery charger to bring them back to fullpower. The charger will provide electricity tothe electrodes (opposite to the direction ofelectron discharge), which will reverse thechemical process within the battery,converting the applied electrical energy intochemical potential energy.

Batteries should only be recharged withchargers that are recommended, by themanufacturer, for that particular type ofbattery. In general, however, battery-industrystandards ensure that any off-the-shelf batterycharger, specified for one brand, size, and type

of battery, will be able to charge correctly anybrand of battery of that same size and type.

Do not, however, use a charger designed forone type of battery to charge a different type ofbattery, even if the sizes are the same. Forexample, do not use a charger designed forcharging “D”-sized Ni-Cd batteries to charge“D”-sized rechargeable alkaline batteries. If in

doubt, use only the exact chargerrecommended by the batterymanufacturer.

Recharging a battery without arecommended charger isdangerous. If too much current issupplied, the battery may overheat,leak, or explode. If not enoughcurrent is applied, the battery maynever become fully charged, sincethe self-discharge rate of thebattery will nullify the chargingeffort.

It is not recommended that batteryusers design and build their owncharging units. Many low-costchargers are available off-the-shelf

that do a good job of recharging batteries.Specific, off-the-shelf chargers are identifiedand recommended, by each of the majorbattery manufacturers, for each type ofsecondary battery they produce.

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The key issue in charging a batteryis knowing when to stop charging.

6.2 CHARGE RATES

The current that a charger supplies to thebattery is normally expressed as a fraction ofthe theoretical current (for a given battery)needed to charge the battery completely in1 hour. This theoretical current is called thenominal battery capacity rating and isrepresented as “C.” For example, a current of0.1 C is that current which, in 10 hours,theoretically, would recharge the battery fully.Table 7 shows some common charging ratesfor various styles of recharging.

6.3 CHARGING TECHNIQUES

In general, lower charge rates will extend theoverall life of the battery. A battery can bedamaged or de-graded if too muchcurrent is appliedduring the chargingprocess. Also,when a battery is inthe final stages ofcharging, the current must be reduced toprevent damage to the battery. Many chargersoffer current-limiting devices that will shut offor reduce the applied current when the batteryreaches a certain percent of its chargedpotential.

Slow charge rates (between 0.05 C and 0.1 C)are the most-often recommended charge rate,since a battery can be recharged in less than aday, without significant probability ofdamaging or degrading the battery. Slowcharge rates can be applied to a battery for anindefinite period of time, meaning that thebattery can be connected to the charger fordays or weeks with no need for special shut-off or current-limiting equipment on thecharger.

Trickle chargers (charge rates lower than0.05 C) are generally insufficient to charge abattery. They are usually only applied after abattery is fully charged (using a greater chargerate) to help offset the self-discharge rate ofthe battery. Batteries on a trickle charger willmaintain their full charge for months at a time.It is usually recommended that batteries on atrickle charger be fully discharged andrecharged once every 6 to 12 months.

Quick and fast charging rates (over 0.2 C) canbe used to charge many kinds of secondarybatteries. In such cases, however, damage ordeterioration can occur in the battery if thesehigh charge rates are applied after the batteryhas approximately 85% of its charge restored.

Many quick andfast chargers willhave current-limiters built intothem that willslowly reduce thecurrent as the

battery is charged, thereby preventing most ofthis deterioration.

The recharge times shown in Table 7 may besomewhat lower than the actual times requiredto recharge batteries at the associated chargerates. Various elements, such as temperature,humidity, initial charge state, and the rechargehistory of the cell, will each act to extend thetime needed to charge the cell fully.

6.4 CHARGING LEAD-ACID BATTERIES

Constant potential charging, with currentlimiting, is usually recommended for sealedlead-acid cells. Due to the sloping voltageprofile of a lead-acid battery, the voltage ofthe battery is a reliable indicator of its state of

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charge. Current limiting may be accomplishedthrough the use of a current-limiting resistor.One manufacturer uses a miniature light bulbas a current-limiting resistor. The brightnessof the bulb will provide a visual indication ofthe state of charge of the battery. In modernpractice, however, current limiting isaccomplished with integrated circuits.

6.5 CHARGING NI-CD BATTERIES

During their recharge cycle, nickel-cadmiumbatteries react in a manner different from otherbatteries. Nickel-cadmium batteries willactually absorb heat during the first 25% ofthe charge cycle (as opposed to mostsecondary batteries, which generate heat allthrough their recharge cycle). Beyond that firstquarter of the charge cycle, a Ni-Cd batterywill generate heat. If constant current isapplied past the point when the battery reachesapproximately 85% of its fully charged state,the excess heat will cause “thermal runaway”to occur. Under thermal runaway conditions,the excess heat in the battery will cause itsvoltage to drop. The drop in voltage will causethe charge rate to increase (according toOhm’s Law), generating more heat andaccelerating the cycle. The temperature andinternal pressure of the battery will continue torise until permanent damage results.

When using trickle or slow chargers to chargeNi-Cd batteries, the heat build-up is minimaland is normally dissipated by atmosphericconvection before thermal runaway can occur.Most chargers supplied with, or as a part of,rechargeable devices (sealed flashlights, mini-vacuums, etc.) are slow chargers.

Quick or fast battery chargers, designedespecially for Ni-Cd batteries, will usually

have a temperature sensor or a voltage sensorthat can detect when the battery is nearingthermal-runaway conditions. When near-runaway conditions are indicated, the chargerwill reduce or shut off the current entering thebattery.

6.6 TIMED -CHARGE CHARGING

Most charging methods, described so far inthis guide, allow the user to begin charging acell regardless of its current state of charge.One additional method can be used to chargeNi-Cd cells, but only if the cell is completelydischarged. It is called the timed-chargedmethod.

One characteristic of Ni-Cd cells is that theycan accept very large charge rates (as high as20 C), provided that the cell is not forced intoan overcharge condition.

The timed-charge charger will provide high-rate current to the cell for a very specificperiod. A timer will then cut off the chargingcurrent at the end of that period. Some cellscan be charged completely in as little as 10minutes (as opposed to 8 hours on a slowcharger).

Great care should be exercised when using atimed-charge charger, because there is noroom for error. If the cell has any charge in itat all at the beginning of the charge cycle, or ifthe cell’s capacity is less than anticipated, thecell can quickly reach the fully charged state,proceed into thermal-runaway conditions, andcause the explosion or destruction of the cell.

Some timed-charge chargers have a specialcircuit designed to discharge the cellcompletely before charging it. These are

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called dumped timed-charge chargers, sincethey dump any remaining charge beforeapplying the timed charge.

6.7 PULSED CHARGE-DISCHARGE

CHARGERS

This method of charging Ni-Cd cells applies arelatively high charge rate (approximately 5 C)until the cell reaches a voltage of 1.5 V. Thecharging current is then removed and the cellis rapidly discharged for a brief period of time(usually a few seconds). This actiondepolarizes the cell components and dissipatesany gaseous buildup within the cell. The cell isthen rapidly charged back to 1.5 V. Theprocess is repeated several more times untilthe cell’s maximum charge state is reached.

Unfortunately, this method has somedifficulties. The greatest difficulty is that themaximum voltage of a Ni-Cd cell will varywith several outside factors such as the cell’srecharge history and the ambient temperatureat the charger’s location. Since the cell’smaximum potential voltage is variable, thelevel to which it must be charged is alsovariable. Integrated circuits are beingdesigned, however, that may compensate forsuch variations.

6.8 CHARGING BUTTON BATTERIES

Secondary cylindrical (household) cells willusually have a safety seal or vent built intothem to allow excess gases, created during thecharging process, to escape. Secondary,button-type batteries do not have such sealsand are often hermetically sealed.

When cylindrical cells are overcharged, excessgases are vented. If a button battery isinadvertently overcharged, the excess gases

cannot escape. The pressure will build up andwill damage the battery or cause an explosion.Care should be taken not to overcharge asecondary button battery.

6.9 INTERNAL CHARGERS

For some applications, the charger may beprovided, by the battery manufacturer, as anintegral part of the battery itself. This designhas the obvious advantage of ensuring that thecorrect charger is used to charge the battery,but this battery-charger combination mayresult in size, weight and cost penalties for thebattery.

6.10 BATTERY TESTERS

A battery tester is a device that contains asmall load and attaches across the terminals ofa battery to allow the user to see if the batteryis sufficiently charged. A simple battery testercan be made from a flashlight bulb and twopieces of wire. Flashlight bulbs are ideal fortesting household batteries, since the voltageand current required to light the bulb is thesame as that of the battery. This kind offlashlight-bulb tester can also be used to draina secondary battery safely before fullycharging it.

Some off-the-shelf household batteries aresold with their own testers. These testers areattached to the packaging material or to thebattery itself. The active conductor in thetester is covered by a layer of heat-sensitiveink. As the ends of the tester are pressedagainst the battery terminals, a small amountof current will flow through the material underthe ink, heating it. The heating will cause theink to change color, indicating that the batterystill has energy.

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Using a simple battery tester to test a Ni-Cdbattery can be somewhat misleading, since aNi-Cd battery has a flat voltage profile. Thetester will indicate near-maximum voltagewhether the battery is 100% charged or 85%discharged.

6.11 “SMART ” BATTERIES

Many battery-powered devices require the useof multi-cell battery packs (i.e., severalordinary battery cells strapped together to beused as a single unit). The individual cellscannot be charged or measured separately,without destroying the battery pack.

A new development in rechargeable batterytechnology is the use of microelectronics inbattery-pack cases to create “intelligent”battery packs. These “smart” battery packscontain a microprocessor, memory, andsensors that monitor the battery’s temperature,voltage, and current. This information can berelayed to the device (if the device is designedto accept the information) and used tocalculate the battery’s state of charge at anytime or to predict how much longer the devicecan operate. The microprocessor on a batterypack may also record the history of the batteryand display the dates and number of times thatit has been charged.

To get the maximum potential from asecondary battery, the user must adopt a strictregimen of noting certain information aboutthe battery and acting upon that information.For example, if a battery is already partiallydischarged, using it in a device will obviouslynot allow the device to be used for its entireduty cycle. Attempting to charge a batterywhen the ambient temperature is too high isanother example of suboptimal battery usage,

since the battery will not hold as much chargeas it would have had it been charged at therecommended temperature.

Most battery users are not sufficiently diligentin matters of battery maintenance. “Smart”batteries allow the battery itself to record allpertinent information and make it available tothe user at a glance.

6.12 END OF L IFE

All secondary batteries will eventually fail dueto age, expended components, or physicaldamage. A battery, when properly maintained,will fail through gradual loss of capacity. Tothe user, this gradual failure will appear as afrequent need to change and charge thebatteries. Sudden failure, usually due tophysical abuse, will prevent the battery fromholding any charge at all.

The physical manifestations of a gradualfailure of the battery can be seen as adegradation of the separator material, dendriticgrowth or other misshapening of theelectrodes, and permanent material loss of theactive components.

The physical manifestations of a suddenfailure, can be seen as the destruction of thebattery components. Open-circuit failure canbe induced by an applied shock to or excessvibration of the battery. As a result, theinternal components of the battery maybecome loose or detached, causing a gap in theelectrical circuit.

Short-circuit failure can be caused by anapplied shock. It can also be caused byoverheating or overcharging the battery. In ashort-circuit failure, some part of one of the

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electrodes pierces (caused by shock) or growsthrough (caused by overcharging) theseparator material in the electrolyte. Thispiercing effect will cause the electrical path tobe shorted.

If a battery and its replacements seem to besuffering repeated premature failures, inreoccurring and similar circumstances, thefailed batteries should be sent to a laboratoryfor dissection and analysis. The problem maylie in faulty equipment, inappropriate batteryusage, or in physical abuse to the device andits batteries. Resolution of the problem willsave time and money in future battery designsand applications.

6.13 BATTERY ADAPTERS

A battery adapter is a device that can be usedinstead of a battery to provide current to abattery-powered device.

Most battery adapters will convert 60 Hz, 110 V, alternating current (i.e., typical housecurrent) into direct current (dc) for use bybattery-powered devices. Other adapters aredesigned to be powered by 12 V automobilebatteries, usually by insertion of a plug intothe automobile’s cigarette lighter.

An adapter will usually have a dc-output plugthat is inserted into the battery-powered deviceto provide dc current to the device.

Usually, manufacturers of the more expensivebattery-powered devices (e.g., cellular phones,laptop computers) will provide the customerwith a battery adapter designed especially forthat device. The adapter will plug into aspecial connector in the device to provide itpower. If designed to do so, the battery adapterwill charge the device’s batteries as well.

Other manufacturers make generic batteryadapters. These adapters will have a battery-shaped appendage that plugs into a battery-powered device in place of a real battery andwill provide energy equivalent to a realbattery. While this kind of adapter has someadvantages (it can be used for any batterypowered device, it can be used when nocharged batteries are available, etc.), thoseadvantages are usually outweighed by thedisadvantages (the power cord is inconvenientand negates the portability of the device, thebattery cover cannot be replaced while thecord is attached, a multiple-battery devicewould require multiple adapters, etc.).

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Battery Manufacturers Web Address

Battery Engineering http://www.batteryeng.com/

Duracell Batteries http://www.duracell.com/

Eveready Batteries http://www.eveready.com/

Kodak Corporation http://www.kodak.com/

NEXcell http://www.battery.com.tw/

Panasonic Batteries http://www.panasonic-batteries.be/home.html

PolyStor Corporation http://www.polystor.com/

Radio Shack http://www.radioshack.com/

Rayovac Batteries http://www.rayovac.com/

Sony Corporation http://www.sel.sony.com/SEL/rmeg/batteries/

Battery Distributors Web Address

Battery-Biz, Inc. http://www.battery-biz.com/battery-biz/

Battery Depot http://www.battery-depot.com/

Battery Network http://batnetwest.com/

Batteries Plus http://www.spromo.com/battplus/

E-Battery http://e-battery.com/

Powerline http://www.powerline-battery.com/

All Web information was verified in August, 1997.

Table 8. Some On-Line Information Available via the World Wide Web

7. Products and Suppliers

Batteries andbatterymanufacturers andsuppliers listed ormentioned in thissection, andelsewhere in thisguideline, are listed for the convenienceof the reader. Thename of a specificproduct orcompany does notimply that theproduct orcompany is,necessarily, the bestfor any particularapplication ordevice. The listsare, necessarily, notall-inclusive. Thelist of Web pageswas compiledfollowing a Websearch performed inAugust, 1997. NewWeb pages mayhave appearedsince then andsome which appear in this list may no longerbe available. Other Web pages, that were notlisted in the Web-search database at that time,will also not appear in this list.

7.1 BATTERY MANUFACTURERS

The battery manufacturers listed below aresome of the manufacturers of householdbatteries. They are presented in alphabetical

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order. All information was verified in August,1997.

7.1.1 Battery EngineeringPostal Address:

Battery Engineering, Inc.100 Energy DriveCanton, MA 02001

Phone Number:(617) 575-0800

Web Page:http://www.batteryeng.com

Email Address:[email protected]

7.1.2 DuracellPostal Address:

Duracell, Inc.Berkshire Corp ParkBethel, CT 06801

Phone Number:1 (800) 551-2355

Web Page:http://www.duracell.com/

7.1.3 EvereadyPostal Address:

Eveready Battery Company, Inc.Checkerboard SquareSt. Louis, MO 63164-0001

Phone Number:1 (800) 383-7323

Web Page:http://www.eveready.com/

Email Address:[email protected]

7.1.4 RayovacPostal Address:

Rayovac CorporationP.O. Box 44960Madison, WI 53744-4960

Phone Number:1 (800) 237-7000

Web Page:http://www.rayovac.com/

Email Address:[email protected]

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8. A Glossary of Battery Terms

2 Ampere-Hour -- One ampere-hour isequal to a current of one ampereflowing for one hour. A unit-quantityof electricity used as a measure of theamount of electrical charge that may beobtained from a storage battery beforeit requires recharging.

2 Ampere-Hour Capacity -- The number ofampere-hours which can be deliveredby a storage battery on a singledischarge. The ampere-hour capacityof a battery on discharge is determinedby a number of factors, of which thefollowing are the most important: finallimiting voltage; quantity ofelectrolyte; discharge rate; density ofelectrolyte; design of separators;temperature, age, and life history of thebattery; and number, design, anddimensions of electrodes.

2 Anode -- In a primary or secondary cell,the metal electrode that gives upelectrons to the load circuit anddissolves into the electrolyte.

2 Aqueous Batteries -- Batteries with water-based electrolytes.

2 Available Capacity -- The total batterycapacity, usually expressed in ampere-hours or milliampere-hours, availableto perform work. This depends onfactors such as the endpoint voltage,quantity and density of electrolyte,

temperature, discharge rate, age, andthe life history of the battery.

2 Battery -- A device that transformschemical energy into electric energy.The term is usually applied to a groupof two or more electric cells connectedtogether electrically. In common usage,the term “battery” is also applied to asingle cell, such as a householdbattery.

2 Battery Types -- There are, in general,two type of batteries: primary batteries,and secondary storage or accumulatorbatteries. Primary types, althoughsometimes consisting of the sameactive materials as secondary types, areconstructed so that only onecontinuous or intermittent dischargecan be obtained. Secondary types areconstructed so that they may berecharged, following a partial orcomplete discharge, by the flow ofdirect current through them in adirection opposite to the current flowon discharge. By recharging afterdischarge, a higher state of oxidation iscreated at the positive plate orelectrode and a lower state at thenegative plate, returning the plates toapproximately their original chargedcondition.

2 Battery Capacity -- The electric output ofa cell or battery on a service test

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delivered before the cell reaches aspecified final electrical condition andmay be expressed in ampere-hours,watt-hours, or similar units. Thecapacity in watt-hours is equal to thecapacity in ampere-hours multiplied bythe battery voltage.

2 Battery Charger -- A device capable ofsupplying electrical energy to a battery.

2 Battery-Charging Rate -- The currentexpressed in amperes at which astorage battery is charged.

2 Battery Voltage, final -- The prescribedlower-limit voltage at which batterydischarge is considered complete. Thecutoff or final voltage is usuallychosen so that the useful capacity ofthe battery is realized. The cutoffvoltage varies with the type of battery,the rate of discharge, the temperature,and the kind of service in which thebattery is used. The term “cutoffvoltage” is applied more particularly toprimary batteries, and “final voltage”to storage batteries. Synonym:Voltage, cutoff.

2 Ci -- The rated capacity, in ampere-hours,for a specific, constant dischargecurrent (where i is the number of hoursthe cell can deliver this current). Forexample, the C5 capacity is theampere-hours that can be delivered bya cell at constant current in 5 hours. Asa cell’s capacity is not the same at allrates, C5 is usually less than C20 for thesame cell.

2 Capacity -- The quantity of electricitydelivered by a battery under specifiedconditions, usually expressed inampere-hours.

2 Cathode -- In a primary or secondary cell,the electrode that, in effect, oxidizesthe anode or absorbs the electrons.

2 Cell -- An electrochemical device,composed of positive and negativeplates, separator, and electrolyte,which is capable of storing electricalenergy. When encased in a containerand fitted with terminals, it is the basic“building block” of a battery.

2 Charge -- Applied to a storage battery, theconversion of electric energy intochemical energy within the cell orbattery. This restoration of the activematerials is accomplished bymaintaining a unidirectional current inthe cell or battery in the oppositedirection to that during discharge; acell or battery which is said to becharged is understood to be fullycharged.

2 Charge Rate -- The current applied to asecondary cell to restore its capacity.This rate is commonly expressed as amultiple of the rated capacity of thecell. For example, the C/10 charge rateof a 500 Ah cell is expressed as,

C/10 rate = 500 Ah / 10 h = 50 A.

2 Charge, state of -- Condition of a cell interms of the capacity remaining in thecell.

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2 Charging -- The process of supplyingelectrical energy for conversion tostored chemical energy.

2 Constant-Current Charge -- A chargingprocess in which the current of astorage battery is maintained at aconstant value. For some types of lead-acid batteries this may involve tworates called the starting and finishingrates.

2 Constant-Voltage Charge -- A chargingprocess in which the voltage of astorage battery at the terminals of thebattery is held at a constant value.

2 Cycle -- One sequence of charge anddischarge. Deep cycling requires thatall the energy to an end voltageestablished for each system be drainedfrom the cell or battery on eachdischarge. In shallow cycling, theenergy is partially drained on eachdischarge; i.e., the energy may be anyvalue up to 50%.

2 Cycle Life -- For secondary rechargeablecells or batteries, the total number ofcharge/discharge cycles the cell cansustain before it becomes inoperative.In practice, end of life is usuallyconsidered to be reached when the cellor battery delivers approximately 80%of rated ampere-hour capacity.

2 Depth of Discharge -- The relativeamount of energy withdrawn from abattery relative to how much could bewithdrawn if the battery weredischarged until exhausted.

2 Discharge -- The conversion of thechemical energy of the battery intoelectric energy.

2 Discharge, deep -- Withdrawal of allelectrical energy to the end-pointvoltage before the cell or battery isrecharged.

2 Discharge, high-rate -- Withdrawal oflarge currents for short intervals oftime, usually at a rate that wouldcompletely discharge a cell or batteryin less than one hour.

2 Discharge, low-rate -- Withdrawal ofsmall currents for long periods of time,usually longer than one hour.

2 Drain -- Withdrawal of current from acell.

2 Dry Cell -- A primary cell in which theelectrolyte is absorbed in a porousmedium, or is otherwise restrainedfrom flowing. Common practice limitsthe term “dry cell” to the Leclanchécell, which is the common commercialtype.

2 Electrochemical Couple -- The system ofactive materials within a cell thatprovides electrical energy storagethrough an electrochemical reaction.

2 Electrode -- An electrical conductorthrough which an electric currententers or leaves a conducting medium,whether it be an electrolytic solution,solid, molten mass, gas, or vacuum.For electrolytic solutions, many solids,and molten masses, an electrode is an

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electrical conductor at the surface ofwhich a change occurs fromconduction by electrons to conductionby ions. For gases and vacuum, theelectrodes merely serve to conductelectricity to and from the medium.

2 Electrolyte -- A chemical compoundwhich, when fused or dissolved incertain solvents, usually water, willconduct an electric current. Allelectrolytes in the fused state or insolution give rise to ions whichconduct the electric current.

2 Electropositivity -- The degree to whichan element in a galvanic cell willfunction as the positive element of thecell. An element with a largeelectropositivity will oxidize fasterthan an element with a smallerelectropositivity.

2 End-of-Discharge Voltage -- The voltageof the battery at termination of adischarge.

2 Energy -- Output capability; expressed ascapacity times voltage, or watt-hours.

2 Energy Density -- Ratio of cell energy toweight or volume (watt-hours perpound, or watt-hours per cubic inch).

2 Float Charging -- Method of rechargingin which a secondary cell iscontinuously connected to a constant-voltage supply that maintains the cellin fully charged condition.

2 Galvanic Cell -- A combination ofelectrodes, separated by electrolyte,

that is capable of producing electricalenergy by electrochemical action.

2 Gassing -- The evolution of gas from oneor both of the electrodes in a cell.Gassing commonly results from self-discharge or from the electrolysis ofwater in the electrolyte duringcharging.

2 Internal Resistance -- The resistance tothe flow of an electric current withinthe cell or battery.

2 Memory Effect -- A phenomenon inwhich a cell, operated in successivecycles to the same, but less than full,depth of discharge, temporarily losesthe remainder of its capacity at normalvoltage levels (usually applies only toNi-Cd cells).

2 Negative Terminal -- The terminal of abattery from which electrons flow inthe external circuit when the celldischarges. See Positive Terminal.

2 Nonaqueous Batteries -- Cells that do notcontain water, such as those withmolten salts or organic electrolytes.

2 Ohm’s Law -- The formula that describesthe amount of current flowing througha circuit.Voltage = Current × Resistance.

2 Open Circuit -- Condition of a batterywhich is neither on charge nor ondischarge (i.e., disconnected from acircuit).

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2 Open-Circuit Voltage -- The difference inpotential between the terminals of acell when the circuit is open (i.e., a no-load condition).

2 Oxidation -- A chemical reaction thatresults in the release of electrons by anelectrode’s active material.

2 Parallel Connection -- The arrangementof cells in a battery made byconnecting all positive terminalstogether and all negative terminalstogether, the voltage of the group beingonly that of one cell and the currentdrain through the battery being dividedamong the several cells. See SeriesConnection.

2 Polarity -- Refers to the charges residingat the terminals of a battery.

2 Positive Terminal -- The terminal of abattery toward which electrons flowthrough the external circuit when thecell discharges. See NegativeTerminal .

2 Primary Battery -- A battery made up ofprimary cells. See Primary Cell .

2 Primary Cell -- A cell designed toproduce electric current through anelectrochemical reaction that is notefficiently reversible. Hence the cell,when discharged, cannot be efficientlyrecharged by an electric current.Note: When the available energy dropsto zero, the cell is usually discarded.Primary cells may be further classifiedby the types of electrolyte used.

2 Rated Capacity -- The number of ampere-hours a cell can deliver under specificconditions (rate of discharge, endvoltage, temperature); usually themanufacturer’s rating.

2 Rechargeable -- Capable of beingrecharged; refers to secondary cells orbatteries.

2 Recombination -- State in which the gasesnormally formed within the battery cellduring its operation, are recombined toform water.

2 Reduction -- A chemical process thatresults in the acceptance of electronsby an electrode’s active material.

2 Seal -- The structural part of a galvaniccell that restricts the escape of solventor electrolyte from the cell and limitsthe ingress of air into the cell (the airmay dry out the electrolyte or interferewith the chemical reactions).

2 Secondary Battery -- A battery made upof secondary cells. See StorageBattery; Storage Cell.

2 Self Discharge -- Discharge that takesplace while the battery is in an open-circuit condition.

2 Separator -- The permeable membranethat allows the passage of ions, butprevents electrical contact between theanode and the cathode.

2 Series Connection -- The arrangement ofcells in a battery configured byconnecting the positive terminal of

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each successive cell to the negativeterminal of the next adjacent cell sothat their voltages are cumulative. SeeParallel Connection.

2 Shelf Life -- For a dry cell, the period oftime (measured from date ofmanufacture), at a storage temperatureof 21(C (69(F), after which the cellretains a specified percentage (usually90%) of its original energy content.

2 Short-Circuit Current -- That currentdelivered when a cell is short-circuited(i.e., the positive and negativeterminals are directly connected with alow-resistance conductor).

2 Starting-Lighting-Ignition (SLI)Battery -- A battery designed to startinternal combustion engines and topower the electrical systems inautomobiles when the engine is notrunning. SLI batteries can be used inemergency lighting situations.

2 Stationary Battery -- A secondary batterydesigned for use in a fixed location.

2 Storage Battery -- An assembly ofidentical cells in which theelectrochemical action is reversible sothat the battery may be recharged bypassing a current through the cells inthe opposite direction to that ofdischarge. While many non-storagebatteries have a reversible process,only those that are economicallyrechargeable are classified as storagebatteries. Synonym: Accumulator;Secondary Battery. See SecondaryCell.

2 Storage Cell -- An electrolytic cell for thegeneration of electric energy in whichthe cell after being discharged may berestored to a charged condition by anelectric current flowing in a directionopposite the flow of current when thecell discharges. Synonym: SecondaryCell. See Storage Battery.

2 Taper Charge -- A charge regimedelivering moderately high-ratecharging current when the battery is ata low state of charge and tapering thecurrent to lower rates as the batterybecomes more fully charged.

2 Terminals -- The parts of a battery towhich the external electric circuit isconnected.

2 Thermal Runaway -- A conditionwhereby a cell on charge or dischargewill destroy itself through internal heatgeneration caused by high overchargeor high rate of discharge or otherabusive conditions.

2 Trickle Charging -- A method ofrecharging in which a secondary cell iseither continuously or intermittentlyconnected to a constant-current supplythat maintains the cell in fully chargedcondition.

2 Vent -- A normally sealed mechanism thatallows for the controlled escape ofgases from within a cell.

2 Voltage, cutoff -- Voltage at the end ofuseful discharge. (See Voltage, end-point.)

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2 Voltage, end-point -- Cell voltage belowwhich the connected equipment willnot operate or below which operationis not recommended.

2 Voltage, nominal -- Voltage of a fullycharged cell when delivering ratedcurrent.

2 Wet Cell -- A cell, the electrolyte of whichis in liquid form and free to flow andmove.

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9. Bibliography

American National Standard Specification forDry Cells and Batteries, AmericanNational Standards Institutes, Inc.ANSI C18.1M-1992.

Application Notes & Product Data Sheet:Primary Batteries—Alkaline, HeavyDuty & General Purpose, RayovacCorporation, January 1996.

Batteries Used with Law EnforcementCommunications Equipment: Chargersand Charging Techniques, W.W.Scott, Jr., U.S. Department of Justice,LESP-RPT-0202.00, June 1973.

Batteries Used with Law EnforcementCommunications Equipment:Comparison and PerformanceCharacteristics, R.L. Jesch and I.S.Berry, U.S. Department of Justice,LESP-RPT-0201.00, May 1972.

Battery Engineering Web Site,http://www.batteryeng.com, August1997.

Battery Selection & Care, Eveready BatteryCorporation, 1995.

Camcorder Battery Pocket Guide, EvereadyBattery Corporation, Inc., 1996.

Cellular Duracell Rechargeable Batteries,Duracell, 1996.

Design Note: Renewal Reusable AlkalineBatteries Applications and SystemDesign Issues For Portable ElectronicEquipment, Rayovac Corporation,presented at: Portable by DesignConference, 1995.

Duracell Batteries Web Site,http://www.duracell.com, August1997.

Easy to Choose, Easy to Use, EvereadyBattery Corporation, 1997.

Encyclopedia of Physical Science andTechnology, Brooke Schumm, Jr.,1992.

Eveready and the Environment, EvereadyBattery Company, Inc., 1995.

Eveready Batteries Web Site,http://www.eveready.com, August1997.

Household Batteries and the Environment,Rayovac Corporation, 1995.

How to Choose, Use, Care For, and Disposeof Batteries, Electronics IndustriesAssociation Consumer ElectronicsGroup, 1992.

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Land Mobile FM or PM CommunicationsEquipment, Measurement andPerformance Standard, ElectronicsIndustry Association/Telecommunications IndustryAssociation, Publication EIA/TIA 603,1993.

Minimum Standards for Portable/PersonalLand Mobile Communications FM orPM Equipment 25-470 MC,Electronics Industries Association,EIA/TIA-316-C-1989.

Navy Primary and Secondary Batteries.Design and Manufacturing Guidelines,NAVSO P-3676, September 1991.

Panasonic Batteries Web Site,http://www.panasonic-batteries.be/home.html, August 1997.

PolyStor Web Page, http://www.polystor.com, August,1997.

Rayovac Batteries Web Site,http://www.rayovac.com, August1997.

Rechargeable Batteries for Personal/PortableTransceivers, National Institute ofJustice, NIJ Standard-0211.01,September, 1995.

Return of the Straight Dope, Cecil Adams,Chicago Reader, 11 East IllinoisStreet, Chicago, IL 60611, 1994.

Supervisory ICs Empower Batteries to TakeCharge, Bill Schweber, EDN, CahnersPublishing Company, 8773 SouthRidgeline Blvd., Highlands Ranch, CO80126-2329, September 1, 1997.

Telephony’s Dictionary, second edition, April1986. Graham Langley, TelephonyPublishing Corp.

The Eveready Battery Story, Eveready BatteryCompany, Inc., 1995.

The Story of Packaged Power, DuracellInternational, Inc., July, 1995.

Van Nostrand’s Scientific Encyclopedia, SixthEdition, Douglas M Considine, Editor,1983.

What is a Battery?, Rayovac Corporation,1995.

Why Use Energizer AA Lithium Batteries?,Eveready Battery Company, Inc., 1993.