Living off the grid and driving an electric car is this former farmer's idea of heaven, page-108

Perhaps getting off topic now, you do not separate to charge, you monitor the performance of each cell using specific gravity and other technical stuff - and when the performance data for an individual cell is dodgy you replace it (in a crisis it can be left out of the circuit if required - I mean, would you notice any real difference between getting punched 221 times, versus getting punched 220 times?). Generally they get replace in large batches, cos it is a very difficult process to remove/replace them . These are not TV remotes.

Just making the point as to why big batteries use individual cells (they are 440volt batteries - you do not tongue test them).
Small batteries are often multi-cell and throw away ..... horses for courses.

All good.