Normally several individual cells are connected together to form a battery pack. Similar to a chain, the weakest link, here the weakest cell, determins the performance of the entire unit. Manufacturing tolerances, different self-discharge rates and much more lead to different remaining capacities of the interconnected cells. To get an efficient system, these differences have to be balanced or avoided. There are two possibilities to solve the problem of a different residual cell capacity in daily practice. Thus, a residual capacity balancing between the cells of a battery pack can be carried out at all, it is necessary to follow some basic rules already during construction of a battery pack:
- Only identical cells from one manufacturer and from one lot (out of one box) may be connected to a stack.
- Never mix up cells with a different past life, a different age or different charge states in a stack.
- Already when buying battery-operated equipment it should be maintained that it has a deep-discharge-protection and an uniform heat load (eg lighting) of the battery pack used, since the self-discharge-rate is temperature dependent. In operation warmer cells lose charge faster than cells which stay cooler. Warmer cells become the weakest link within a short period of time, which leads, in the worst case, to an useless battery pack.
continue reading --> Charging an accumumulator stack