Lead-acid storage batteries have long been an efficient and effective source of power for a variety of applications. From every indication it is clear that such batteries will continue in heavy use into the indefinite future. While much work has been done to develop nickel-cadmium batteries, nickel-iron batteries, lithium, sodium-sulphur systems and other electrochemical storage systems, and other alternative power sources, lead-acid batteries remain and are likely to remain the best choice for strong reasons, including their relatively low cost.
The economy and dependability of lead-acid storage batteries makes such batteries practical for a vast number of applications, including stand-by power systems for communication and emergency lighting, automotive and truck-starting applications, electric vehicles, wheel chairs, uninterruptable computer power supplies, and systems for solar and wind power storage, to name just a few.
Maximum flexibility in the design of the lead-acid battery is desirable because such batteries have so many varied applications and uses. Having the ability to position the battery terminals in different portions of the battery case greatly increases the number of design variations and alternative embodiments possible to the designer and seller.
A significant disadvantage to conventional lead-acid storage battery construction is the many separate electrical connections which must be made within the battery as separate welding operations. Conventional lead-acid storage batteries have intercell connections inside the battery just under the top wall. Such connections are typically made by separately welding an upstanding projection from a plate bridge of one cell to an upstanding projection from the plate bridge of the adjoining cell. The weld is through a hole in the battery container partition between cells. In a 12-volt post-style battery there are five such welds. These welds are typically made above the top of the plates in the headspace of the battery.
In addition to the intercell weldments in separate operations, plate groups within each battery cell are welded to their respective plate bridge along the tops of the plates. Another separate welding operation is incurred in welding the bridges of the first and last cells not connected to the inner cell. Thus, there are a substantial number of welds within the battery. The process of making these welds and connections is time consuming, unduly expensive and includes the possibility of miswelds and broken welds.
Conventional lead-acid batteries also use relatively large amounts of lead. Preferably, the use of lead should be minimized because of the effect of lead on humans. Therefore, when use of lead is necessary or beneficial, it is well accepted that use of less lead is desirable because that implies less human exposure to lead at all stages of production and use--both of the raw material itself and of the lead-containing product. It is likewise desirable to minimize human exposure by the nature of product design and the nature of manufacturing methods.
In the field of lead-acid batteries, progress has been made in recent years in reducing the handling of lead and exposure to lead in battery production. For one thing, progress has been made in recovering, recycling and reusing lead used in the manufacture of storage batteries; 96.8% is recovered according to 1991 data available from The Battery Council International. Among the advances more directly related to battery production methods are mechanization of welding operations and reduction of lead dust in manufacturing facilities.
Despite recent progress, there is a continuing need for improvements to reduce the amount of lead used in lead-acid storage batteries, to further reduce or eliminate human contact with lead in battery production and, more generally, to further reduce human exposure and health concerns related to lead use in storage batteries.
Another consideration or shortcoming with respect to lead-acid batteries has been their substantial weight or, stated differently, an energy density which is relatively low because of the heavy weight of the battery. This shortcoming is a particular concern in applications in which the power supply must be mobile, such as electric-powered vehicles, where total vehicle weight is a factor determining and limiting vehicle range.
Everyone concedes or would concede that it is wasteful and environmentally unsound to use more lead than necessary in batteries. It is also known that long electrical paths increase the internal resistance of the battery and, as a result, decrease its energy density. Certain limited progress has been made in recent years in shortening the electrical path from the battery cells to the external battery terminals. This has been done mainly with certain "through-the-partition" cell connectors and the use of external side terminals.
Yet there is a long-standing unsatisfied need in the field of lead-acid storage batteries for batteries which have a still shorter electrical path and which, in whatever way, are substantially lower in weight and higher in energy output than the conventional lead-acid storage batteries of recent years.
Certain of the above problems and shortcomings have been addressed in earlier work, including the disclosures of U.S. Pat. No. 3,261,719. The device of such patent has lead-receiving cavities in its base which extend from one cell to an adjacent cell and provide electrical union. The case of such device has side walls and partitions which are unitary with the top wall, and this structure is essentially glued to the base by the insertion of epoxy over the lead and most of the base in position to join with the walls and partitions.
The device of U.S. Pat. No. 3,261,719, while it does address certain problems has leakage potential because of its method of manufacture. Because of the construction of such device, heat sealing by ultrasonic welding, or other modern methods, is not easily done. Furthermore, its method of manufacture has too many steps, and is therefore potentially slow and costly. The invention was never used commercially.
Thus, the many problems noted above have remained unsolved. There is an important, long-standing need for improvement in lead-acid batteries.