It'll just lose power very gradually, but really you never fly them long enough for that to happen. You can do 5-7 minutes easy on most setups, and batteries aren't near as temperamental as an engine.

I still consider getting a nitro every once in a while, but I already have a nice charger and electrics have better power to weight and reliability so...I dunno. I don't think nitro/gas helis have anything going for them at this point beyond aesthetics.