This must be a common problem, but I'm just not 100% on what to try next. My Tangerine ibook will sometimes shut off when running on battery power. When I reboot it, the time/date gets set back to like 1969 or something crazy...it doesn't happen all the time though. The battery seems to hold a charge and it'll run on battery power OK sometimes. Also, it won't boot on battery power alone once it's cutout...it has to be plugged in to the charger before I can reboot. Could this be the charger board? I've tried all the reset options that the apple site recommends, and I downloaded some power manager patch or something...nothing's worked so far.
BTW...replaced the 3GB HD with a 40GB 5400rpm Hitachi drive...Highly recommended...although not an easy job. The battery issue existed before all that.