What difference does it make what he charges it with?
this is a topology question.
"2 x 6nr 2v cells wired in series to form two 12v cells and then these two 12v cells wired in parallel to give 12v.
or:
6 x 2nr 2v cells wired in parallel to form six 2v cells and then these wired in series to give 12v."
Given one 'bad' or 'weak' cell, the former instance is more reliable because it will result in the failure of just that one cell, rather than the good cell it is paired with as well.
However if you know for a fact they are all matched it really makes no difference until you have at least 50-100 cells, then its a statistical gamble, and you need individual cell monitoring to find the weak ones before they die.