my 12" rev. B powerbook is 9 months old. It used to have good battery life, but it has been declining (to be expected, I guess). Tonight, with only itunes and camino running, the battery lasted only about 1.5 hours, at which point it was at 21%, showing ~40 min more of life. Then, it just crashed. From 21% to zero in one second. It's fine now that it's plugged back in... but why did this happen? It didn't used to happen... advice? thanks!