I see no reason why it wouldn't work, just rip out the mains connection and solder a wire from the +ve on the meter to the +ve on the charger and do the same with the negs. You might get a weenie (and I mean weenie) bit of voltdrop but not enough to be upsetting. It'd still be good enough to tell you when its battery charging time.
I've not had one apart but I wouldn't have thought soCheers was just worried the spring mechanism might be part of the board