We did exactly this to our PA28 a couple of weekends ago. My instructor colleague found it with the master on when he took it out of the hangar. He said 'let's charge the battery for an hour', but I didn't heed his advice and started the a/c using jump leads and the PA28 coaxial socket. Initially it showed a normal charge but gradually the charge rate went up and the CB tripped at 60 amps. We let things cool off a bit and then put the battery on charge for 3 hours. After that time, we had an off-charge battery voltage of 12.4V (giving time for the 'float' voltage to subside). The aircraft then started normally and showed a usual charge rate for the rest of the day. The battery doesn't seem to have suffered at all from this experience and after about another 20 hours of flying all seems OK. The battery is about 600 flying hours old.
Lesson learned for me: listen to a wiser head even though it might have delayed things a bit. Doing it my way, we lost one more revenue flight and a slightly p*ssed-off student. My bad.
TOO