EP1027745A1

EP1027745A1 - Sealed battery and method of operation

Info

Publication number: EP1027745A1
Application number: EP98946048A
Authority: EP
Inventors: Boris Tsenter
Original assignee: Ultra Force Battery Co
Current assignee: Ultra Force Battery Co
Priority date: 1997-09-11
Filing date: 1998-09-11
Publication date: 2000-08-16
Also published as: WO1999013523A1; AU9315098A

Abstract

A sealed rechargeable battery affords the advantages of both vented batteries and sealed batteries while avoiding the disadvantages of each. Power cells (12) constitute a rechargeable energy source. Regulator cells in the form of metal-hydride cells (18) operate in tandem with the power cells. A hydrophobic barrier separates the power cells from the metal-hydride cells, and prevents migration of water and electrolyte, but allows the migration of gases such as hydrogen and oxygen between the two sets of cells. A voltage stabilizer (14) monitors the metal-hydride cells via a programmed microprocessor (16). By detecting the direction and amount of current flowing through the metal-hydride cells, the voltage stabilizer monitors the operation of the power cells. When current flows in one direction, oxygen is produced by the power cells and absorbed or consumed by the metal-hydride cells. When current flows in the opposite direction, hydrogen is consumed. By applying certain voltages to the metal-hydride cells, the voltage stabilizer controls their operation to enhance the performance of the power cells.

Description

SEALED BATTERY AND METHOD OF OPERATION

TECHNICAL FIELD

The present invention relates generally to sealed rechargeable batteries and to an operation method for such sealed rechargeable batteries

BACKGROUND ART

The following documents are wholly and completely incorporated herein by this reference thereto: U.S. Patent No. 5,143,799, U.S. Patent No. 5,290,640, U.S. Patent No. 5,569,554, and U.S. Provisional Patent Application No. 60/058,557, all associated with the present inventor. ιo Industrial sealed batteries are constructed according to two general designs:

1. A series-connected design with individual cells; and

2. A common vessel design.

A series-connected sealed cell needs strong control of individual cells, especially if the cell capacity is more than 10-15 Ah. Such control creates operational is problems and requires replacement of individual cells periodically.

The common vessel design is generally attributed to lead acid of secondary batteries (VRLA) capable of consuming oxygen at a low rate and with the accompanying production of a small amount of hydrogen. On the one hand, the low rate of oxygen consumption allows the use of a common gas space without a

∞ significant capacity imbalance associated with oxygen consumption. On the other hand, hydrogen production and the impossibility to consume hydrogen require using a regulated valve to vent the explosive hydrogen gas.

The major advantage of the VRLA is the use of a common vessel for all battery cells and the possibility of using one valve for providing safety features for

25 whole battery. The disadvantage of this design is the periodical thermal runaway of individual cells and the rise of battery impedance. Both of these phenomena are caused by electrolyte loss. Indeed, the loss of electrolyte in the process of off-gassing results in an increase in the rate of oxygen consumption inside of cells as oxygen is generally not replenished.

Electrolyte loss causes the battery impedance to rise. It is very important at this point to keep the electrolyte balance in VRLA. Electrolyte decomposition is associated primarily with hydrogen production since no mechanism for hydrogen consumption exists in a VRLA battery.

U.S. Patent No. 5,569,554 (incorporated herein by this reference thereto) teaches that a sealed rechargeable battery with a common gas space is capable of consuming hydrogen and oxygen. Such operation is provided by a special metal- hydrogen regulator in gas communication with working cells but without electrical or electrolytic contacts with the working cells.

As set forth herein, the working cells are abbreviated PPC for Power Produced Cells. The metal-hydrogen regulator cells are designated as MHC (Metal Hydrogen Cells) regardless of whether metal or metal-oxide electrodes are used in regulator. The prior patent (5,569,554), opened the way to create a large-scale sealed battery, but suffers from the following shortcomings;

1. It does not specify a method of connection for the MHC;

2. It does not specify an optimum electrolyte for either the PPC or the MHC; and 3. It does not take into consideration the imbalances in the PPC caused by the gas consumption process.

While U.S. Patent No. 5,569,554 is directed to an improvement of prior designs, the improvement disclosed therein is associated with the introduction of a voltage stabilizer maintaining a preselected voltage range to the MHC. The '554 device, taking into consideration the chemistry MHC, does not optimize voltage depending upon what gas (oxygen or hydrogen) is being consumed.

The background set forth above indicates the need for a battery that is sealed and requires no maintenance and is free from the shortcomings of the above- mentioned patents. DISCLOSURE OF INVENTION

The present invention provides a sealed battery and a method of operation for a rechargeable sealed battery where the maintenance and gas hazards of the vented battery and size limitation and thermal management problems of the sealed battery are eliminated.

Improvements achieved in the battery covered by the present invention are related to the use of electrochemical, metal/metalhydride - hydrogen control cells for detection of oxygen and hydrogen gases generated during the charging and discharging in the battery cells. The control cells are also capable of consuming oxygen and hydrogen when excess amounts of gases are generated. By detecting gas generation and by stopping charging when the battery cells are fully charged, electrolyte decomposition in the battery cells is eliminated and there is no need to refill the cells with water.

The present invention is directed to an improved design for a sealed battery having a common gas space.

The present invention is also directed toward excluding any non electrical battery maintenance during extended battery operation while keeping high battery performance at the same time.

The present invention provides use of a voltage stabilizer with two levels of voltage: one voltage value for oxygen consumption and one voltage value for hydrogen consumption. The voltage stabilizer operation is based on the consideration that the optimum voltage level for hydrogen consumption differs from the optimum voltage level for oxygen consumption. Exploitation of this voltage difference can be used to monitor and control the charging and discharging of the battery. The present invention connects MHCs in series. The series-connected MHC cells provide many more benefits in comparison with parallel-connected cells. Indeed the ratio of PPC: MHC is 1:5 as a rule. This means that the MHCs consume approximately five times more current than is produced in the gas-generated reaction in PPCs. The individual cell voltage for the MHC is relatively small. The combination of small voltage and big current create a problem for voltage stabilizer design overcome by the present invention.

The advantages realized by a series-connected MHC are not obvious and are based on the considerations associated with oxygen and hydrogen cycles. Connection of MHCs in series is based on the fact that cell overdischarge does not adversely affect MHC performance.

The invention further provides a procedure for rebalancing PPCs. The imbalance problem is caused by gas production inside of the PPCs and gas migration from the PPC to the MHC. Some consumption of the migrating gas occurs in the MHC. Oxygen production on the positive electrode of Ni-Cd battery and consumption of that oxygen in the MHC results in an accumulation of metallic cadmium on the cadmium electrode PPC. This electrode imbalance leads to hydrogen production prior to oxygen production in the process of battery charging.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a block diagram of a sealed rechargeable battery system with an integrated control cell constructed according to the present invention. FIG. 2 shows a procedure for rebalancing the PPC. FIG. 3 shows the relationship between battery voltage and current through the

MHC in the process of discharging and overdischarging PPC.

MODE(S) FOR CARRYING OUT THE INVENTION

FIG. 1 illustrates an electrical diagram for realization of the present invention. The primary power supply 10 serves as a power supply for the PPC and the voltage stabilizer 14. The voltage stabilizer 14 provides two levels of voltage stabilization for MHC depending on which gas (hydrogen or oxygen) is being consumed. The voltage stabilizer 14 passes current in two directions depending on the gas consumed. The regulation of current through the battery by means of a power regulator, stabilizer management, and temperature and pressure management is provided by a control unit 16 (generally, a microprocessor). The control unit 16 receives feedback indicating current and voltage of the PPC 12 and the MHC 18 as well as from separate temperature 30 and pressure 32 sensors. The invention may use two levels of voltage stabilization: one level for hydrogen consumption and a second level for oxygen consumption. The need for two levels is caused by the adverse effect high voltage has on operating parameters of cells. Assuming the use of metal-hydride/hydrogen chemistry on the MHC 18, and

5 assuming the voltage is equal to 0.4V/cell (as chosen per U.S. Patent No. 5,569,554), if the hydrogen is consumed by the MHC, everything is well and the PPC 12 is operating properly. However, if oxygen is consumed under this voltage, the metal- hydride electrode can corrode because of the relatively small difference (only 0.4V) between the metal-hydride electrode and the stationary oxygen electrode. o Increased cell voltage adversely affects the rate of hydrogen consumption on the hydrogen electrode because of oxygen absorption. It is clear from this consideration that one compromise voltage value for the MHC does not provide either corrosion resistance or a maximum rate of gas consumption. Consequently, there is need to operate with two voltage levels depending on what gas is being consumed, s oxygen or hydrogen.

Hydrogen consumption requires an overvoltage equal to approximately 0.05 < h < 0.2V/cell. The required voltage value per cell is the cell open circuit voltage (OCV) minus the overvoltage. A metal-hydride hydrogen cell with an OCV value equal to 0 (zero) needs a voltage of 0.05 < h < O.2V/cell for hydrogen 0 consumption. The cadmium-hydrogen cell (OCV = 19mV) needs voltage equal to

0.030 < h < 0.18V cell. A zinc-hydrogen cell with an OCV equal to 0.42V needs a voltage of 0.37 < h < O.22V/cell for hydrogen consumption.

If an MHC is used with a metal oxide as a positive electrode (anode), the rule is the same. A nickel-hydrogen coupled with an OCV equal to 1.3V needs 1.25 < h 5 < l. lV/cell for hydrogen consumption, for example.

The oxygen consumption process needs more voltage for prevention of heat dissipation in the MHC 18. Indeed the OCV (E_Q) of oxygen-metal-hydride couple is 1.23 V. The heat dissipation in this case can be estimated roughly as the product of (Eo-V)I. Consequently, in order to decrease heat dissipation the stabilizer voltage o must be increased for increased oxygen consumption. In the other words, instead of heat dissipating inside the MHC 18, it will dissipate inside the voltage stabilizer 14. The optimum overvoltage for oxygen consumption is O.5 < h < 0.7V. The stabilizer voltage should be set at a level approximately the same as the OCV of metal-oxygen couple minus the overvoltage for oxygen consumption. The voltage for an oxygen metal-hydride MHC should be 1.23 - (0.5-0.70) = 0.5 < V < 0.7/cell. For an oxygen-zinc MHC with an OCV equal to 1.65V, the stabilizer voltage should be 1.65 - (0.5-0.7) = 0.95 < V < 1.15/cell. The beneficial use of a two-level voltage stabilizer that depends on consumed gas is possible as a method of gas recognition is known and realized through the present invention. The voltage stabilizer 14 supports both of the two voltage levels as set forth herein.

The direction of the current (positive to negative or vice versa) is an indicator as to whether oxygen or hydrogen is being consumed. Hydrogen consumption is associated with current direction (electron flow) through the MHC from the positive to the negative terminals of the stabilizer, if a metal-hydrogen couple is used in the MHC. The current travels in the opposite direction in the case of oxygen consumption. For metal oxide-hydrogen chemistry, when used as the MHC, it is vice versa.

The microcontroller determines what gas is consumed based on current direction measurements and responsively applies the appropriate stabilizer voltage value.

Connection of the MHC in series is based on the consideration that reversing the potential on a cell does not adversely affect battery operation. The probability of cell reversal is high for a multicell long battery string. Assuming that the metal- hydride-hydrogen chemistry is used in the MHC and assuming also that one cell reverses polarity, this cell produces hydrogen or oxygen or both depending on what electrode is in reverse polarity. Hydrogen or oxygen are consumed in the other cells according to the present invention and do not create any problems associated with increased pressure or the escape of gas. If one cell of the MHC is in reverse polarity under a gas-generated current, and that current is equal to I, and the total number of series-connected cells is N, then every MHC cell will additionally consume I/(N-1) amount of gas, only an incremental amount. Water lost from reversed polarized cells with the gases returns back to the cell through the common gas space in order to equalize the difference in electrolyte concentration. Having a difference in the concentration of electrolytes in the PPC and the MHC is based on the fact that in some cases it is necessary to have one electrolyte optimized for the PPC and a second electrolyte optimized for the MHC.

A nickel-metal-hydride PPC needs a mixture of potassium and lithium hydroxides for high charge efficiency with the nickel-oxide electrode. The metal- hydride-hydrogen MHC only needs a potassium hydroxide electrolyte because it does not contain a nickel-oxide electrode. The unique circumstance of having two different electrolytes arises from the absence of electrolytic contact between two electrolytes. The electrolytes then have only one kind of exchange flow — the water vapor flow. The two electrolytes should have the same water vapor pressure initially to prevent significant electrolyte concentration imbalance. This water pressure value can be calculated and the vapor water pressure will be corrected automatically by means of water vapor exchange between two electrolytes in common gas space.

Fig.2 shows a procedure for the rebalancing of a 5 cell 100 Ah PPC. The rebalancing process is associated with corresponding reactions in the PPC and the MHC. For a Ni-Cd battery as the PPC and MH-H₂ couple used as the MHC, the overall reaction is: l/2Cd + NiOOH + H₂0 — > l/2Cd (OH)₂ + Ni(OH)₂ (1)

The reaction caused with hydrogen production on the nickel-oxide electrode as 0 a result of electrode imbalance is generally the same as in reaction (1) on the cadmium electrode: l/2Cd + H₂0 — > l/2Cd (OH)₂ + 1/2H₂ (2)

The same amount of hydrogen is consumed in the MHC as per reaction: 1/2H₂ + Me⁺ — > MeH (3) s Hydrogen production creates a negative voltage in the cell. The negative voltage value depends on the current density and has range of (-0.1) - (-0.4)V/cell. A battery composed of 5 cells has a negative voltage equal to -1.6 V, roughly (- 0.32V/cell), as illustrated in Fig. 2. As soon as the cadmium electrode capacity is depleted, the process of cadmium discharge is substituted by a process of oxygen o production with a corresponding rise in negative battery voltage.

The control unit 16 (microcontroller) is programmed to provide the proper rebalancing cycle according to the kind of gas being initially consumed. If hydrogen is initially consumed, this indicates that the negative electrode of the PPC has exceeded its charging capacity and is producing hydrogen. The PPC needs rebalancing according to the procedure set forth herein. The voltage on the PPC is negative during the rebalancing procedure according to above-mentioned considerations.

Fig. 3 shows the relationship between battery voltage and current through the MHC in the process of discharging and overdischarging the PPC. The initial current is close to zero, because no gas production has occurred from the beginning of the discharging. As soon as individual cells in the battery string go to an overdischarging state, as per reaction (2), hydrogen gas is produced and consumed in the MHC. The gas pressure rises slightly and reaches a stationary level when the rate of hydrogen production from the overdischarging cell is equal to the rate of hydrogen consumption in the MHC. As illustrated in Fig. 3 of the present invention, total battery discharging voltage can drop below l.OV/cell and the design can survive despite the overdischarging of individual cells. The lowest battery voltage is 3.1V (Fig. 3) in this case and battery pressure is sufficiently low.

The approach set forth herein gives great advantages over present sealed rechargeable battery designs. First of all, the battery's energy capacity can be used completely. Secondly, electrolyte decomposition in individual cells does not affect its operation. Concentrated electrolyte will be diluted due to water vapor adsorption from the common gas space. Third, the MHC uses the PPC as a power supply which greatly simplifies the total electrical circuitry.

The present invention uses a method of hydrogen refilling. The battery can lose hydrogen during valved off-gassing and through the natural slow leakage of hydrogen that often occurs through a plastic housing or the like. Hydrogen leakage leads to an MHC imbalance resulting in an inability to consume oxygen. The rise in oxygen pressure along with the low oxygen current indicates the necessity of providing a hydrogen refill. The present invention accommodates hydrogen injection through a battery inlet and the consumption of hydrogen as per reaction (3), for example.

Energy is supplied by means of a power supply rectifier 10 and a current regulator 42 to battery or battery cells connected in series. The power can be either linear or switching power depending on the battery application. A power transistor is used as a current regulator 42 and is managed by the control unit 16. The control unit 16 may be a microcontroller with a predetermined bit word length, 2 or more A/D converters, a serial part and a memory with a predetermined capacity.

5 The control unit 16 monitors the voltage, current, and temperature of the battery 12, the current and current direction in the control cell 18, and, by means of transducers 30, 32, the temperature and pressure within the sealed container 44. These input parameters are used to manage the current regulator 42 and the voltage selector 40. The output voltage from the voltage selector 40 varies with the type of ιo gas that is being consumed in the control cells 18. The control cell 18 also signals the current regulator 42 to adjust the charging current as soon as hydrogen is detected in the control cells 18.

The battery cells 12 in the present invention have commonly-used battery chemistries with metal or metal-hydride as negative cathode electrodes and metal- i5 oxide as positive anode electrodes. NiMH, NiCd, and NiZn chemistry battery cells have nickel-oxide as their positive electrode. Characteristic of this type of electrode is that it has 100% charge efficiency up to a state of charge of 90-95%. This is particularly true for modern designs of nickel-ore electrodes, i.e., sintered, foam and fiber electrodes. Consequently, oxygen production does not occur during charging

20 until the electrode has reached a state of charge of 90-95%.

When the electrode is overcharged with an additional 5-10% capacity, a large amount of oxygen is produced, resulting in electrolyte decomposition. The oxygen formed is consumed in the control cells, but the oxygen consumption also leads to overheating of the control cells which adversely affects their operation. The

25 electrolyte decomposition transfers water from the battery cells 12 to control cells 18. With the present invention, the control cells detect when oxygen starts to be produced which triggers termination of battery cell charging or lowering of charging current to a predetermined level. The control cells sense when the batteries are fully charged.

₃o The detection of oxygen production is done by monitoring the current flow in the control cells. The direction of control cell current flow under a predetermined voltage of the control cells from the negative to the positive terminals of the control cells indicates oxygen production (and battery overcharging). The volume and pressure of oxygen and the amount of current in the control cells 18 depend on the rate of oxygen production and/or consumption. As soon as the control unit (via the control cells) recognizes current direction flow and a preselected current value, the charging is terminated or reduced. By preventing the overcharging of the batteries, electrolytic integrity is preserved, battery life prolonged, and battery performance enhanced.

Another function of the control cells is to consume oxygen and hydrogen. When oxygen is produced during charging, the oxygen is consumed at the hydrogen electrode in the control cells. This causes an imbalance in the battery cells as the negative electrodes accumulate the excess of the charged capacity. The excess capacity causes hydrogen production in the battery cells and consumption of hydrogen in the control cells. If the control cells indicate hydrogen consumption prior to oxygen consumption, this is a signal to provide an equalization charge to the battery cells. This equalization charge can be provided with relatively low average current equal to C/100 > I > C/10 Amps but with a high amplitude current.

A low average equalization charge current prevents the control cells from overheating and the high amplitude charge current enhances the high level of state of charge for the nickel-oxide battery electrode. Periodic full charge of the nickel-oxide electrode is beneficial for operational stability with respect to battery life cycle.

Equalization charge is continued until stable values of battery voltage and pressure are reached, as well as constant current value and temperature of the control cells. The stable value of these parameters indicate that the equalization charge of the battery cells is completed and the charging energy is only related to electrolyte decomposition in the battery cells.

A voltage selector unit 40 receives feedback from the control cells for selecting the optimum voltage at which oxygen and hydrogen are consumed at maximum rates. The feedback from the control cells is the current direction flow. The direction of the current flow depends on what gas is produced in the battery cells and consumed in control cells. As the optimum voltage is different for oxygen and hydrogen, it is necessary to provide different voltage levels, depending on type of gas consumed. For the metal-hydride hydrogen chemistry in the control cells, the optimum voltage for hydrogen consumption is O.1-O.4V. The optimum voltage for oxygen consumption is O.5-O.8V. If the voltage for hydrogen is used for oxygen consumption, too much heat would be generated as per the formula (E-V) x I watt. Another negative effect arising from using the lower hydrogen voltage for oxygen consumption is corrosion of the metal-hydride cathode because of the difference between the potential of metal-hydride cathode and the stable potential of the hydrogen electrode in an oxygen atmosphere is too small. On the other hand, an excessively high voltage for hydrogen consumption will have an adverse effect on hydrogen consumption rate because of oxygen absorption. As per the above, it is imperative to select the proper voltages for the control cells as related to the type of gas being consumed. As heat has a negative effect on the control cells, voltages for oxygen and hydrogen must be selected which minimize heat dissipation in the control cells. When the optimum voltages for gas consumption in control cells are selected, the heat dissipation is transferred from the control cells to the voltage selector unit.

To prevent penetration of electrolyte from the battery cells into the control cells, a hydrophobic separator is used. A separator with small hydrophobic pores is placed between the top of the battery cells and the bottom of the control cells. When small amounts of electrolyte particles adhere to the gas generated during charging of the battery cells, they are stopped by the small pores of the hydrophobic separator from entering into the control cells and will drop down into the electrolyte in the battery cells. On the other hand, the gases from the battery cells can penetrate easily through the separator and reach into the control cells. This approach prevents flooding of the control cells which are operated under starved electrolyte conditions. The pore size for the hydrophobic separator can be determined by the Laplace formula:

P = 2σ cos a , r where: p = capillary pressure; σ = surface tension; = tension angel; and r = pore radius.

INDUSTRIAL APPLICABILITY

The present invention provides a large rechargeable sealed battery that requires no maintenance. It also provides an electrochemical control cell(s) within a sealed battery to manage the charging and discharging of the sealed battery. Additionally, the present invention provides a means of charging the battery while minimizing the decomposition of the electrolyte. Furthermore, the present invention provides a hydrophobic separator between the battery cells and control cells that prevents the flow of electrolyte between such cells but allows the flow of gas in either direction between such cells.

Another object of the present invention is to determine what gases, either oxygen or hydrogen, are being consumed in the MHC. For such determination, the present invention uses detection of the current's direction across the MHC.

Another object of the present invention is to use two different electrolytes: one for the PPC and one for the MHC. These two chemistries operate for different functions, with the PPC for energy production and the MHC for gas consumption (and accompanying pressure and thermal management). The two different functions require use of two different electrolytes. A sodium hydroxide electrolyte, as an example, is used for a nickel-cadmium application in a hot climate. It is impossible to use a sodium electrolyte in an MHC as this electrolyte does not support gas consumption. Instead, MHC operates with a potassium hydroxide electrolyte.

Another object of the present invention is to provide conditions for full battery discharge by means of gas consumption by a cell in reverse polarity with respect to battery discharge. This is a very important operation issue because cells with low capacity do not limit the total battery capacity as in the case of a string of individually sealed cells.

These and other objects, advantages, and the industrial utility of the present invention will be apparent from a review of the accompanying descriptive specification, claims, and drawings.

Claims

What is claimed is:

A sealed rechargeable battery, comprising: a battery cell, said battery cell rechargeably supplying electric power; a regulating control cell, said regulating control cell having a hydrogen electrode, said regulating control cell in gaseous, but not liquid, communication with said battery cell; a voltage stabilizer, said voltage stabilizer in feedback communication with said regulating control cell, said voltage stabilizer detecting direction of current flow in said regulating control cell according to the consumption of oxygen and/or hydrogen by supplying voltage at at least two levels; and a control circuit, said control circuit monitoring status of said battery cell and said regulating control cell, said control circuit controlling operation of said voltage stabilizer; whereby better battery operation and performance is obtained by monitoring and controlling said regulating control cell to prevent overcharging and electrolyte decomposition.

A gas regulated rechargeable storage battery comprising: a gas exchange housing; a rechargeable working cell within said gas exchange housing, said working cell having working cell electrodes; a first electrolyte inside said working cell; a first ratio between charging and discharging capacities of said working cell electrodes; a rechargeable metal-hydrogen cell witbin said gas exchange housing said metal-hydrogen cell having metal-hydrogen cell electrodes; a second electrolyte inside said metal-hydrogen cell; a second ratio between charging and discharging capacities of said metal-hydrogen cell electrodes; a voltage stabilizer coupled to said metal-hydrogen cell, said voltage stabilizer capable of supporting two levels of constant voltage across said metal-hydrogen cell; and a pressure inlet for hydrogen injection; whereby operation and performance of said rechargeable working cell may be monitored and controlled by said metal-hydrogen cell as controlled by said voltage stabilizer.

3. The battery according to claim 2, wherein said metal-hydrogen cell is one of a plurality of metal-hydrogen cells connected in series.

4. The battery according to claim 2, wherein the current direction across said metal-hydrogen cell is used for recognizing hydrogen and/or oxygen consumption.

5. The battery according to claim 4, wherein a current direction is from a positive terminal to a negative terminal of said metal-hydrogen cell when hydrogen is consumed.

6. The battery according to claim 5, wherein said current direction is from said negative terminal to said positive terminal of said metal-hydrogen cell when oxygen is consumed.

7. The battery according to claim 6, wherein said metal-hydrogen cells are supported under a voltage per cell equal to a metal-oxygen cell open circuit voltage minus (0.5-O.7)V when oxygen is consumed.

8. The battery according to claim 6, wherein said metal-hydrogen cells are supported under voltage per cell equal to a metal-hydrogen cell open circuit voltage minus (0.05-0.2)V when hydrogen is consumed.

9. The battery according to claim 2, wherein said first electrolyte is an optimum electrolyte for working cells under a condition of equal partial water vapor pressure for said first and second electrolytes.

10. The battery according to claim 2, wherein said second electrolyte is optimum electrolyte for metal- hydrogen cells.

11. The battery according to claim 2, wherein hydrogen consumption occurring prior to oxygen consumption is used to indicate a need for a rebalance cycle.

12. The battery according to claim 2, wherein a rebalance cycle is provided by means of overdischarging working cells until a negative voltage of approximately -(0.4-0.5)V/cell is reached and consumption of hydrogen occurs in said metal-hydrogen cells simultaneously.

13. The battery according to claim 2, wherein rising of battery pressure during oxygen consumption is used to indicate a need for a refilling cycle.

14. The battery according to claim 2, wherein said metal-hydrogen cells are refilled by external hydrogen injection through said battery inlet and by charging said metal-hydrogen cells simultaneously.

15. The battery according to claim 2, wherein a regulating voltage is applied during battery discharge.

16. The battery according to claim 2, wherein a rechargeable working cell is selected from the group consisting of: nickel-cadmium, nickel-metalhydride, nickel-zinc, silver-zinc, nickel-iron, manganese-zinc and lead-acid (Pb-PbO₂) rechargeable working cells.

17. The battery according to claim 2, wherein said metal-hydrogen cell is selected from the group consisting of: cadmium-hydrogen, metalhydride-hydrogen, zinc-hydrogen, iron-hydrogen, lead-hydrogen, nickel oxide-hydrogen, and lead dioxide- hydrogen cells.

18. A method of operating a sealed rechargeable battery having at least one battery cell, at least one control cell in gaseous communication with said battery cell, and a voltage selector, said control cell having a metal or metal- hydride electrode and a hydrogen electrode, said electrodes being connected to said voltage selector, said method comprising the steps of: detecting oxygen or hydrogen by means of current direction in said control cell; and based on detection of oxygen or hydrogen, selecting appropriate charging parameters or recommending termination of discharging.

19. The method of operating a sealed rechargeable battery according to claim 18, wherein during charging of the battery, said steps further comprising: detecting current at a preselected level and a direction of current flow in the control cell from a negative to a positive terminal; based on said level and direction of current flow in the control cell, terminating charging; detecting a reversed direction of current flow from said positive to said negative terminal in the control cell; and based on said reversed current, initializing an equalization charge by reducing a charging current to a preselected value and continuing charging until reaching stable parameters, battery voltage, and pressure, as well as an appropriate temperature and constant current in the control cell.

20. The method of operating a sealed rechargeable battery according to claim 19 wherein during discharging of the battery, the steps further comprise: detecting said reversed direction of current flow in the control cell from said positive to said negative terminal; and based on said reversed current, recommending termination of battery discharge.