My 2G i-Phone battery life suddenly dropped to just a few hours with hardly any use. It first I thought the battery just suddenly failed, but I also noticed that it was getting very hot at random without doing anything.
I read that applications could be running continuously at maximum processor power eating the battery. I tried un-installing every app, one at a time to see if it would help but no success. I eventually re-rain Redsnow but still no change.

Bottom line, I restored the phone through i-Tunes, then ran Redsnow and that cured everything!

Just wanted to pass this useful information. I know this is a common problem.