No, the BIOS battery only keeps track of time when the system is off. The rest of the time it's done by your operating system. If your computer is constantly screwing up on the time it's either A) you have too much crap running in the background or B) there's a bug in Windows XP that the auto time updating is screwed up. Try changing it to time.nist.gov instead of the microsoft server. That sometimes help. Otherwise, just disable the automatic time.