Individual batteries are typically too small in terms of either storage capacity or voltage. Storage capacities often need to be increased to deal with battery maintenance issues or to extend operating times for attached loads. Voltages may need to be increased to reduce system amperage through various components or to meet charge controller requirements. Reaching the necessary electrical system requirements can be easily accomplished by connecting the batteries in the appropriate manner.
To recall, series wiring results in voltages adding and amperage remaining the same while parallel wiring results in amperages adding and voltages remaining the same.
Wiring the batteries up to achieve the necessary capacity is akin to the internal battery wiring used to create the battery itself from the individual cells. Special consideration must be paid to this external interconnection however. A key design goal for battery banks is to maintain all components to be as identical as possible so as to reduce wear on the batteries. This includes:
- Interconnection cable length
- Battery capacities
- Interconnection fuse ratings
Addressing the above concerns, variation in cable length will cause different resistances between batteries. This will lead to disproportionate charging between bank members. Likewise, differing capacities will cause the batteries to constantly attempt to equalize with one another leading to early battery death.