The manufacturer for by A123 and LIFE batteries say 2,0v per cell is cut off. So in a 4 cell pack that is 8v, the charger wont work there, when it shuts off the battery is ok, the charger wont get hurt... In our flight packs we leave margins so that we dont run out at some point above Terra Firma.... Not necessary in these field packs. I have used a sullivan starter on one of these that was used on capacity... just like your power drill... about time you notice something is low in voltage it is done... time to recharge. Good morning Dennis!