But these things happen. I left one on for six months once and had to replace the whole wiring harness as the cells leaked. A day or two on the other hand will not significantly damage a pack in most cases. A good 48 hour slow charge will usually bring them back. OK, class dismissed.
Lets go flying.
I only had it on to check the transmitter and servos for probably less than 10 minutes. For long term storage I would recommend that the pack be removed and stored in the refrige. Not real easy on the 4NBF as you have to remove the back and unplug the pack from the jack next to the switch and then snake out the wires past the charge jack. Anyway I found some extra Y connectors and viola, a light went off. At the same time I could be doubling my reliability, unless of course something happens to one of the packs that drags the other down to nothing.