Ibook G4 Battery Problems


I have an iBook G4 that worked fine. After upgrading to Tiger, I begin experiencing a rare problem. If I use my mac with the battery only after a while or after being sleep and I wake it, the screen turns gray, and it does not respond to anything, I have to remove the battery, plug it in, reset the PMU and restart. So it won't run on battery only. So I called Apple and they sent me a brand new battery. First 2 days it worked fine, but then back to the same problem. Any clues??