Week 8 Multi cell Battery Pack

We can understood this through an illustration. Let's assume a connection of cells with weakest cell as labelled below in the electrical coonection diagram of a battery pack

Now, since it is the weakest cell it will reach cut-off voltage earliest. Thus, as soon as it reaches cut-off voltage , no more current can flow in the same branch since it will discharge the cell more. Now, this series branch has become useless. Also, more current can't flow in the rest of battery pack since, because if it will flow then this series branch will also have to supply the current. In short, whole battery pack can't supply the current even though other cells have charge left in them. Thus, the weakest cell has limited the usable capacity of whole battery pack. It's similar analogy to : chariot speed being limited by the weakest horse.

Solution : The solution is to balance the capacity of the cells so that there is no significant difference in their individual capacities. Balancing can be of two types either active balancing or passive balancing. This can be done through battery management system (An Able Charioteer), which can provide additional charge of stronger cell to weaker cell or may deploy any other method. In this way, weakest cell won't affect the battery usable capacity.