How to Charge the Ni-Cd Battery?

Ni-Cd Battery and Ni-MH Battery are amongst the hardest batteries to control. Whereas with lithium ion batteries and lead acid batteries it is possible to control overcharge by setting a maximum charge voltage, the nickel based batteries do not have a"float charge" voltage. So the charging relies on forcing current through the battery. The voltage to do this is not fixed in stone like it is for another batteries.

This makes these cells and batteries particularly hard to charge in parallel. That is because you can't be confident each cell or package is the exact same impedance (or resistance), so some will require more current than others even when they're full. This means that you will need to use a separate charging circuit for each string in a parallel package, or balance the current in another manner, for example using resistors of such a resistance it is going to control the current control.