RE: Hey, who knows what about voltage regulators
MJD -
I doubt if it would need a sink - the voltage differential is small and current demands are relatively low and sporadic. The 78xx series will hold a peak current of around 2.4 A. If we were running more than 3 servos, I would probably be inclined to look for a slightly higher current rating, just to manage a stalled servo more than anything. For 2s lipos, I think one of the LDO Vregs might be a better choice.
BTW, I cobbled up a constant current charger like you - primarily to form charge NiMH packs. None of my chargers would drop low enough for forming my 350 and 400 mAh packs.