BACKGROUND OF INVENTION One problem frequently encountered with batteries of all types is the loss of charge during periods in which the battery is not used; this can be a particular problem with certain high power batteries. The extent to which loss of charge over time is problematic is a function of the chemical reactions within the cell and the physical design of the battery, especially the electrodes. A second problem involves recharging a battery after periods of deep discharge and/or providing a single power source which is capable of satisfying the various current demands for differing applications.

Because lead-acid batteries remain a predominant device for delivering electrical current in many electrical operations, the problems just described have particular import as related to such batteries. Lead-acid batteries retain their popularity as an electrical energy source because they can be manufactured easily and relatively inexpensively, are rechargeable and are capable of delivering relatively high power. They also can withstand rugged treatment and can be stored for extended periods.

There are two major classes of lead-acid batteries. Conventional lead-acid batteries such as valve-regulated lead-acid batteries are typically comprised of a plurality of cells. Each cell typically includes a set of interleaved monopolar positive and negative

electrodes or plates which are separated by a porous separator. The electrodes or plates are typically composed of a lead or lead alloy current collector and an electrochemically active paste which is coated onto the exterior surfaces of the current collector. In conventional lead-acid batteries, the current collectors are in the form of a grid and are relatively thick. In newer improved lead-acid batteries, the current collectors are made of ultra-thin films or foils (lead or lead alloys) which are wound into a"jelly roll" configuration. The development of such batteries has been pioneered by the assignee of the current invention and the particular design features of such batteries are described in U. S. Patent 5,047,300, U. S. Patent 5,045,086 and U. S. Patent 5,368,961. Batteries utilizing such thin plate design are referred to by the assignee of the current invention as "Thin Metal Foil"batteries, or simply"TMF"batteries. Lead-acid batteries of this design are capable of very high discharge and recharge rates. The thin plate design means that such batteries are also significantly lighter and smaller than their conventional counterparts.

Like other batteries, lead-acid batteries, including those of the TMF design, are susceptible to losing charge during periods in which they sit idle. Loss of charge over time is affected by a process called"self-discharge"--chemical reactions within the battery which cause the consumption of electrolyte, even when the battery is not exposed to an external load. The consumption of electrolyte through self-discharge decreases discharge capacity because the discharge capacity of a battery is proportional to the specific gravity, or concentration, of electrolyte within the battery. Thus, self-discharge reduces the shelf life of the battery (i. e., the period of time during which the battery maintains sufficient discharge capacity for its intended purpose when the battery is allowed to sit idle without having to provide current to an external load), but it also results in voltage decay (i. e., a decrease in open circuit voltage).

As indicated above, the ability of a battery to retain charge while sitting idle is dependent in large measure on the chemistry within the battery, especially the chemical reactions that occur at the interface between the current collector and the paste. With certain current collectors, especially pure lead and low-tin alloy current collectors, a passivation layer can form at this interface. The passivation layer reduces the process of

self-discharge but negatively impacts cycle life (the number of discharging and recharging cycles a battery can sustain while still delivering a certain level of electricity).

Other current collectors, such as those containing higher levels of tin for instance, form a conductive or semi-conducting layer at the current collector/paste interface. While such batteries have good cycle life, the improved cycle life comes at the cost of a decrease in shelf life.

Thus, one approach for dealing with the loss of battery charge during periods of non-use has been to vary the composition of the current collectors in an effort to optimize both shelf life and cycle life. As alluded to above, however, increases in shelf life typically occur at the expense of cycle life. Other approaches have included instructing the user of the battery to recharge the battery at regular and frequent intervals. This approach is not convenient and also generally requires a corded power source to recharge the battery. Consequently, there remains a need for an apparatus and methods which can maintain high power battery functionality for long periods of time without requiring user maintenance and a corded power supply.

It is also desirable to have a dual battery assembly using lead-acid batteries wherein one battery can recharge the other after periods of deep discharge and wherein the two batteries have different discharge capabilities to meet the differing current requirements of various applications. In dual battery assemblies designed to meet this specific need, the first battery generally has a high discharge rate but relatively low capacity; the second battery has a low discharge rate but high capacity. For instance, a dual battery assembly of the design just described would be useful in recharging a battery that was drained during periods of extended use without recharging or otherwise weakened (e. g., a battery drained when car lights are inadvertently left on or a battery whose performance is reduced because of the cold). In such a case, the first battery with its high discharge rate can be used to"jump"the depleted battery; the second battery with its lower discharge rate and higher capacity can be used to recharge the first battery. A dual battery assembly of this type is also useful because the first battery can provide high levels of current within a short time period for applications requiring such current, whereas the second battery can be used to deliver current to devices requiring low levels

of current for extended time periods (e. g., personal entertainment devices such as radios and televisions).

Several different dual battery systems have been described including U. S. Patent 5,223,351 to Wruck, U. S. Patent 2,616,937 to Kullgren, U. S. Patent 5,614,331 to Takeuchi et al., U. S. Patent 5,565,756 to Urbish et al., U. S. Patent 4,770,954 to Noordenbos, U. S. Patent 5,194,799 to Tomantschger, U. S. Patent 3,165,689 to Hughes, 5,352,966 to Irons, U. S. Patent 3,883,368 to Kordesch et al., European Patent 370534 B I to Witehira, German Patent 1005142, Canadian Patent 2,171,603 to Maston, et al., abstract of Japanese patent J06078465, abstract of Japanese patent J03210775, PCT publication W098/40926, European application 513531 A1, and German application 19611776 Al. However, none of these dual battery systems are believed to include all the features of the dual batteries of the present designs described herein, especially those designs wherein inexpensive batteries are used to maintain the state of charge of high powered batteries.

SUMMARY OF INVENTION The present invention satisfies the needs identified above by providing dual battery systems of varying design but which generally include a first battery that is connected in parallel to a second battery. In certain embodiments, the second battery can recharge the first battery after discharge of the first battery. The second battery can also be used to provide current for those applications which require low levels of current over extended periods, while the first battery can be used in situations in which a high level of current must be generated over a short time period. In other embodiments, the second battery is connected in a circuit so that it supplies a low-level current that maintains the charge of the first battery that otherwise would undergo a relatively rapid loss of charge over time due to the process of self-discharge. Various embodiments are particularly useful as portable power supplies which can be used to jump start cars and/or power various personal devices which require lower levels of current.

More particularly, in embodiments wherein the dual battery system is capable of providing two levels of current, the system includes: (i) a first battery, (ii) a second

battery, and (iii) a circuit connecting the first and second battery in parallel. In general, the first battery in such embodiments has a relatively high power density as compared to the second battery, whereas the second battery has a higher energy density (i. e., capacity) than the first battery. Thus, the first battery is selected so as to have a first peak amperage which exceeds the second peak amperage of the second battery. The first battery also has a faster discharge rate than that of the second battery. The first battery may also have a self-discharge rate which is greater than the corresponding rate for the second battery.

Finally, the second battery is also typically of lower cost than the first battery.

In another aspect, the present invention provides dual battery systems having the same general design of that just described but with additional components to control current flow through the assembly. More specifically these embodiments include the necessary elements to restrict current so that it only flows from the second battery to the first battery; the current may be further restricted so that it is sufficient to maintain the charge of the first battery during periods of non-use, but insufficient to provide current to an external load. Embodiments of this general design comprise: (i) a first battery having a first energy density (capacity) and (ii) a second battery having a second energy density which is greater than the first energy density of the first battery, (iii) an electrical circuit which connects the first and second battery in parallel and (iv) a current direction regulator connected to the circuit which functions to prevent current from passing from the first battery to the second battery. Typically, the current direction regulator is a diode, although other circuitry or devices which limit current flow in the desired manner could be used as well. In this manner, it is possible to maintain the state of charge of the first battery without user intervention for significantly longer periods than if the first battery was simply left alone.

The dual battery system in these embodiments may also include a current level controller which limits the function of the second battery to only passing a very low level of current for the maintenance of the state of charge of the first battery. The current level controller may be a resistor but other circuitry or devices restricting the amount of current flow from the second battery to the first battery could be utilized instead. Thus, in contrast to the embodiments which do not include the current direction regulator and

current level controller, the second battery in this alternative embodiment is prevented from participating in the functional capability of the first battery, i. e., the current level controller prevents the second battery from passing current to an external load.

The first battery and second battery in these embodiments have the same characteristics as the first and second batteries discussed above in those embodiments which lack the current control elements. Additionally, because the current direction regulator prevents current from flowing from the first battery to the second battery, it is possible for the open circuit voltage (OCV) of the second battery to initially be less than that for the first battery. This contrasts with the typical situation in which the OCV of the second battery exceeds the OCV of the first battery. Dual battery assemblies using first batteries having a higher OCV can be used, for instance, when the self-discharge rate of the first battery is sufficiently faster than that of the second battery so that at some point after the two batteries are connected the OCV voltage of the second battery exceeds that of the first battery. This type of arrangement could also be utilized if the voltage of the first battery decreased more rapidly with discharge than the second battery.

Dual battery systems which incorporate the current control elements provide several advantages. First, dual battery assemblies of these designs provide a cost effective way to extend the fundamental charge retention characteristics of a high power battery. Using the dual battery system of these designs, it is possible to increase the charge retention of high-power batteries by at least two times or more. In fact, by replacing the second battery, it is possible to extend the functional life of the first battery almost indefinitely. Furthermore, the dual battery systems provided by the present invention alleviates the need to frequently recharge the first battery and avoids having to use corded electrical sources to recharge the first battery.

Regardless of the particular embodiment, the first battery can be of a variety of types but most preferably is a lead-acid battery, a nickel cadmium battery or a nickel hydride battery, although batteries of different chemistries could also be used. The first battery is preferably a lead-acid battery, especially one utilizing ultra-thin current collectors or plates. The negative current collector, and preferably the positive current collector as well, are preferably 0.005 inches or less thick. It is also preferred that at least

the positive current collector. and optionally the negative current collector, be a substantially non-perforated foil. The positive and negative current collectors may be coated on their two major faces with paste to yield a plate; these plates are preferably 0.010 inches thick or less. Batteries using such ultra-thin plates and/or current collectors are referred to as Thin Metal Foil cells, or simply TMF cells.

The second battery in the different embodiments can include a variety of different battery types, including, but not limited to, a lead-acid battery or an alkaline battery. If the second battery is a lead-acid battery, it preferably is of a conventional design wherein the current collectors are lead or lead alloy grids. In certain preferred embodiments, however, the second battery is an alkaline cell or collection of alkaline cells. The use of alkaline batteries is advantageous because of their low cost and because they are energy dense.

In an especially preferred embodiment, the dual battery assemblies described herein include an alkaline cell or cells as the second battery and a TMF cell or cells as the first battery. The combination of these batteries when connected in parallel produces an assembly in which the unique power capabilities of the TMF battery can be made available on demand over a long period of time without any external maintenance by the user of the dual battery assembly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a pictorial view of a dual battery assembly according to a preferred embodiment of the present invention.

FIG. 2 is a pictorial view of a dual battery assembly according to another preferred embodiment of the present invention wherein a diode and resistor are included within the circuit that connects the batteries in order to control current flow between the two batteries.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides two major embodiments of a dual battery system, each designed to solve particular problems associated with battery power supplies. The

first major embodiment is useful for providing a unified system wherein a first battery can be recharged by a second battery after the first battery has been subjected to deep discharge. Assemblies of this first type are also useful in providing current for applications which require a high amount of current over a short period of time (first battery function) and for providing current to other applications which only require low levels of current but for extended periods of time (second battery function).

In a variation on the design just described, the present invention further provides a dual battery assembly which utilizes a second battery and various current control components to maintain the functionality of the first battery for significantly longer periods of time than if the first battery was simply allowed to undergo the normal process of self-discharge. The apparatus and methods of the present invention can achieve these results using cost effective and readily available second batteries and do not require user maintenance or a corded source of electricity. In both of these major embodiments, the term"battery"as used herein is meant to include assemblies containing a single cell or a collection of cells.

With reference now to FIG. 1, one general design for the apparatus of the present invention is depicted. The dual battery assembly generally includes a first battery 10 and a second battery 40. The first battery 10 includes a positive terminal 12 and a negative terminal 14. Likewise, the second battery 40 includes a positive terminal 20 and a negative terminal 18. The first battery 10 and second battery 40 are connected at their respective terminals by connector 16 and connector 26 to form a circuit, wherein the first battery 10 and second battery 40 are connected in parallel. External loads can be attached at terminals 15 and 25.

The second battery 40 can be enclosed in a housing 30 in order to provide a convenient means for handling the cell or cells that comprise the second battery 40.

Similarly, the cell or cells that make up the first battery 10 can be placed within a housing (not shown) to facilitate ease in handling. It is also possible to include both the first battery 10 and the second battery 40 within a single housing. The positive and negative terminals of the first battery 10 and second battery 40 may be connected to positive and

negative terminals, respectively, positioned on the exterior of a case which is designed to hold both batteries.

In certain embodiments of the general design depicted in FIG. 1, the first battery 10 has a first peak amperage and the second battery 40 has a second peak amperage, wherein the peak amperage of the first battery 10 exceeds that of the second battery 40, particularly with respect to size and weight. Preferably, the first battery 10 and the second battery 40 are capable of being recharged. It is preferred that the peak amperage of the first battery 10 be sufficient to start an automobile engine by itself, or in combination with the second battery 40. Ideally, the first battery 10 is capable of delivering sufficient power to start a car engine several times before needing to be recharged. In contrast, the second battery 40 is characterized by having a higher energy density (i. e., higher capacity) than the first battery 10. The capacity of the second battery 40 is such that the second battery 40 can deliver relatively low levels of current at many different times without requiring recharging between uses. Thus, the first battery 10 is characterized as having a high power density, while the second battery 40 is characterized by having a high energy density.

In certain embodiments, the first battery 10 also has a first open circuit voltage (OCV), and the second battery 40 has a second OCV which is greater than the OCV of the first battery 10 of the second battery 40. A design of this type results in a low-level current which flows from the second battery 40 to the first battery 10, thereby maintaining the state of charge of the first battery 10 that would otherwise be lost through the normal self-discharge reactions that are associated with the first battery 10. In another aspect, the self-discharge rate of the first battery 10 is greater than the corresponding rate for the second battery 40. This means that the shelf-life of the second battery 40 is longer than the shelf-life of the first battery 10 (shelf-life referring to the time during which the battery maintains sufficient discharge capability for its intended purpose when the battery is allowed to sit without use).

In addition to these characteristics, in the general embodiment shown in FIG. 1, the first battery 10 and the second battery 40 are selected so that the second battery 40 has the necessary capacity to recharge the first battery 10 after the first battery has been

discharged. In general this means that the nominal voltage of the two batteries are roughly equivalent; furthermore, the voltage of the second battery 40 preferably does not decrease as rapidly with discharge as compared to the voltage decrease associated with discharge of the first battery 40. Thus, after the dual battery system is used, the voltage of the second battery is sufficiently greater than the voltage of the first battery so that the second battery can recharge the first battery.

Although the first battery in FIG. I is shown as being comprised of 6 individual cells, it should be appreciated that the exact number of cells is not critical to the present invention. The number of cells can be varied according to the particular performance characteristics that are desired for each application. Likewise, the manner in which the individual cells comprising the first battery 10 are interconnected is not a critical aspect of the invention. For instance, the cells can be connected in series or in a parallel configuration depending upon the specific performance criteria which are required. The same is true for the second battery 40. While FIG. 1 depicts 9 individual cells as comprising the second battery 40, here too, it should be understood that the exact number of cells and the connections there between can be varied according to the particular demands of the application for which the dual battery assembly is to be used.

The first battery 10 can be any of a number of different battery chemistries so long as the criteria set forth above are satisfied. For instance, the first battery may be a lead-acid battery, a nickel cadmium battery or a nickel hydride battery. In particularly preferred embodiments, the first battery 10 of the present invention includes lead-acid batteries such as those described in U. S. Patent 5,047,300 to Juergens, U. S. Patent 5,045,086 to Juergens and U. S. Patent 5,368,961 to Juergens; these patents are assigned to the assignee of the present invention and are incorporated by reference herein.

Batteries of these designs are characterized by having ultra-thin current collectors and pasted current collectors or plates. The plates or foils in such batteries are spirally wound. Batteries having the characteristics described in these patents are referred to by the assignee of the current invention and referred to herein as being TMF (Thin Metal Foil) cells or batteries.

Briefly, batteries of the TMF design include ultra-thin current collectors and plates. The negative current collector, and optionally the positive current collector, in TMF cells typically are 0.005 inches thick or less. It is also preferred that the positive current collectors, and preferably the negative current collectors as well, are substantially non-perforated. The term"substantially non-perforated"is defined herein to mean that the foil is essentially a solid film of metal rather than existing as a grid which is the traditional form for current collectors used in lead-acid batteries. The term allows for the possibility, however, that the foil or film may include a very limited number of small holes therein. Given their shape as ultra-thin foils, the positive and negative current collectors each have two major faces which can be coated with a layer of paste. The combination of the current collectors and layers of paste are referred to as"plates"within the industry. The paste thickness of each layer applied to the current collectors is 0.005 inches or less thick and preferably 0.002 to 0.003 inches thick. Thus, the negative plates, and optionally the positive plates, are typically 0.010 inches thick or less. In certain embodiments, however, the foil and plates may be thicker. For example, in some embodiments the foil may be 0.008 inches or less thick and the plate may be 0.015 inches or less thick.

Preferably, the positive and negative current collectors or plates in the battery are cast on to positive and negative end connectors which separately join the positive and negative current collectors or plates. Details of the end connector design can be found by reference to U. S. Patent 5,198,313 to Juergens, which is assigned to the assignee of the present invention and is incorporated herein by reference.

The second battery 40 can be selected from batteries which have the characteristics set forth above. In certain embodiments, the second battery may include conventional lead-acid batteries which utilize current collectors of the standard grid design which are also thicker than those found in the TMF design.

Plates in conventional lead-acid batteries are formed by forcing paste into the interstices of the grid. The plates are thicker than those of the TMF design; the plates may be 0.05 inches thick or greater for example. Although conventional lead-acid batteries cannot achieve the discharge rate of TMF batteries, they have the advantage of

being able to store more capacity in a smaller size and with less weight and cost as compared to the TMF batteries.

Conventional lead-acid batteries are one preferred type of battery for the second battery because of their low cost relative to TMF batteries. In other preferred embodiments, however, the second battery 40 is an alkaline cell, such as a zinc manganese dioxide cell that is available from any of the major commercial battery manufacturers. The use of alkaline cells in the second battery 40 is preferred because of their low cost, high energy density and low self-discharge characteristics. It would also be possible to use a nickel cadmium, lithium or metal hydride battery.

Because the second battery 40 preferably has a high energy density, it is not necessary to store all the required capacity in the first battery 10. The dual battery assembly of the design described may undergo significant idle periods between use.

During these idle periods, energy is transferred from the second battery 40 to the first battery 10, thereby putting the first battery 10 at full charge for subsequent applications.

Thus, in general, increased capacity in the second battery 40 is desirable; the capacity of the second battery 40 should be greater than that of the first battery 10. For example, the capacity of the second battery 10 may be approximately 10 times that of the first battery 10; however, other capacity ratios can be used.

In certain embodiments, both the first and second batteries 10,40 may be lead- acid batteries, with the distinction being that the first battery 10 is of the TMF design while the second battery 40 is of conventional design. Other embodiments, however, may involve combinations of different battery types. When utilizing batteries of differing electrochemistries, it is important for proper functioning of the assembly that the batteries have essentially the same nominal voltage. Those skilled in the art will recognize that by correctly connecting individual cells in parallel or series, varying different nominal voltages can be obtained as desired.

In a particularly preferred embodiment, the dual battery assembly comprises a first battery 10 that is of the TMF design and a second battery 40 that is an alkaline battery. These embodiments are particularly useful because the combination of the TMF battery and alkaline battery yields a dual battery assembly in which the high power and

rapid discharge characteristics of the TMF battery can be made available for extended time periods without any external maintenance by the user of the assembly. These embodiments in which the first battery 10 is a TMF battery and the second battery 40 is a conventional lead-acid battery or series of alkaline batteries are particularly useful as portable power supplies because such combinations can generate very high peak amperages and high discharge rates (first battery) while still having high capacity (second battery), all in a combination which is relatively inexpensive and modest in weight and size.

An alternative embodiment is illustrated in FIG. 2. The dual battery assembly of this design is quite similar to that shown in FIG. 1. The assembly differs in that the circuit connecting the two batteries includes a current direction regulator 22 and may also include a current level controller 24 to control the direction and amount of current flow between the two batteries 10,40. Assemblies having the design depicted in FIG. 2 are designed to maintain the charge of the first battery during extended periods of non-use.

As with the embodiment depicted in FIG. 1, the dual battery assembly shown in FIG. 2 generally includes a first battery 10 and a second battery 40. The first battery 10 includes a positive terminal 12 and a negative terminal 14. Likewise, the second battery 40 includes a positive terminal 20 and a negative terminal 18. The first battery 10 and second battery 40 are connected at their respective terminals by connector 16 and connector 26 to form a circuit, wherein the first battery 10 and second battery 40 are connected in parallel. An external load can be connected at terminals 15,25.

This general embodiment also includes a current direction regulator 22 within the circuit that connects the first battery 10 and the second battery 40. As depicted in FIG. 2, the current direction regulator 22 can be connected in series between the positive terminals 20,12 of the second and first batteries 40,10, respectively. The current direction regulator 22 prevents current from flowing from the first battery 10 to the second battery 40; instead, the current direction regulator 22 keeps current only flowing from the second battery 40 to the first battery 10. When the current direction regulator 22 functions in this manner, the state of charge of the first battery 10 can be maintained without user intervention for substantially longer periods than if the first battery 10 was

functioning independently. As shown in FIG. 2, the current direction regulator can be a diode. However, the current direction regulator could be other devices, circuitry or means which restrict current so that it only flows from the second battery 40 to the first battery 10.

A current level controller 24 can also be included within the circuit that joins the first battery 10 and the second battery 40 as further shown in FIG. 2. The current level controller 24 can be connected in series within the circuit between the positive terminal 20 of the second battery 40 and the positive terminal 12 of the first battery 10.

Preferably, the current level controller 24 is used in conjunction with the current direction regulator 22 and is positioned within the circuit between the current direction regulator 22 and the positive terminal 12 of the first battery 10. The current level controller 24 limits the amount of current that can pass from the second battery 40 to the first battery 10.

More specifically, the current level controller 24 preferably restricts current flow from the second battery 40 to the first battery 10 to a level which is sufficient to maintain the charge of the first battery 10 but insufficient to participate in the functional capability of the first battery 10 (i. e., the second battery does not produce current for an external load).

Said differently, the current level controller 24 acts to ensure that the first battery 10 operates within its rated capabilities without any current discharge contribution from the second battery 40. Thus, dual battery assemblies of the design shown in FIG. 2 function somewhat differently than the assembly shown in FIG. 1 in that the second battery 40 does not deliver current to an external load.

The current level controller 24 can be a resistor as shown in FIG. 2 However, other circuitry, devices or means which similarly restrict the level of current flowing to the first battery 10 can be utilized as well.

The general characteristics of the first battery 10 and the second battery 40 are generally the same as those described above in the description of the embodiment shown in FIG. 1. As indicated above, the OCV of the second cell typically is greater than the OCV of the second cell; this results in a low-level of current flowing from the second battery 40 to the first battery 10 to maintain the state of charge of the first battery 10.

However, in certain embodiments of the type shown in FIG. 2, the OCV of the first

battery 10 may initially exceed the OCV of the second battery 40. The current direction regulator 22 in these instances ensures that current still does not flow from the first battery 10 to the second battery 40. In such cases, the voltage of the first battery 10 must drop below that of the second battery 40 before the second battery 40 can recharge the first battery 10. This could occur, for example, when the self-discharge rate of the first battery 10 is sufficiently faster than that of the second battery 40 so that at some point after the batteries are connected the OCV of the second battery 40 is greater than that of the first battery 10. An arrangement of this type would also work in those cases wherein the voltage of the first battery 10 decreased more rapidly with discharge as compared to the second battery 40.

As to chemical type, the first battery, can include any of the types described in relation to FIG. 1, including for instance a lead-acid, nickel cadmium or nickel metal hydride battery. Preferably, the first battery 40 is a lead-acid battery, and more preferably is of the TMF design. The second battery 40 may be a conventional lead-acid battery, or more preferably is an alkaline battery because of their small size and low cost. In particularly preferred embodiments, the first battery 10 is a lead-acid battery, especially one of the TMF design and the second battery 40 is an alkaline battery.

Using a system in which the first battery 10 is of the TMF design and the second battery 40 includes a series of alkaline cells such as can be bought from any commercial supplier, it is possible to extend the shelf-life of the first battery 40 by at least a factor of 2. Of course, if the inexpensive alkaline cells are replaced, it is possible to maintain the shelf-life, and thus access to the high power performance of the TMF first battery, essentially indefinitely.

The present invention also provides methods for maintaining the charge state of high power batteries. The methods generally comprise connecting a first battery 10, a second battery 40, and a current direction regulator 22 to form an electrical circuit wherein the first battery 10 and the second battery 40 are connected in parallel; the current direction regulator is connected in series between the first and second battery 10, 40.

The method can further include connecting a current level controller 24 into the circuit in order to restrict the amount of current flow from the second battery 40 to the first battery 10. The current level controller is connected in series with the first and second battery 10,40. The current level controller 24 acts to limit current flow from the second battery 40 to a level which maintains the charge on the first battery but which is insufficient to provide current to an external load.

As discussed above, current direction regulator 22 may be a diode or other means which prevents current flow from the first battery 10 to the second battery 40. The current level controller 24 can be a resistor or similar means for achieving the same effect.

The particular type of first battery 10 and second battery 40 is not particularly critical so long as the batteries have the characteristics described above in relation to FIGS. I and 2. The methods preferably include connecting a first battery 10 such as a lead-acid, a nickel cadmium or a nickel hydride cell with a second battery 40 which is preferably a lead-acid battery of conventional design or an alkaline battery. Most preferably, a lead-acid battery of the TMF design is connected with an alkaline battery.

All of the references listed herein are incorporated herein by reference.