Minn,
Man, I know that feeling sometimes. Not that I mind it though. I've actually gone to the field on some nights and not taken any of my own planes, but still flew pretty much non-stop.

Most of my battery packs are too hard to get to, so just replacing them is a pain. It's easier to just plug a charge cord in to the side of the plane and let it top off while I re-fuel and BS a little.

How long your pack lasts depends a lot on how you fly, and how long you fly. I'm only getting about 1hr of actual air time on a charge with my Cap, but the flying isn't exactly sedate either. I also reach for the charge cord when my pack reads 4.8 or less. Some guys will fly on lower, but since I have the field charger, it's just easier to not worry about it.