First point, correct your schematic. No battery is charged by an unlimited voltage source, neither single nor multiple cells.
I'm not sure which battery type you imagine for "3V"? Curiously you have drawn multi cell battery symbols, even with different cell count…
In other words, I would appreciate a clear and consistent question.
Generally there's a problem with charging in series circuit if the individual cells aren't guaranteed to have exactly the same capacity and initial state of charge. With lead-acid batteries, it's usual to charge multiple cells in series. Li-Ion batteries in contrast need balancing circuits, they are built-in with any battery on the market, e.g. notebook batteries.