The battery wouldn't slow down pages at all, the way to tell if your battery is gone is to check that the system clock isn't way off (and doesn't keep track of time when the PC is off).
I'm not sure why your PC didn't adjust the time automatically, there may be a settings in WinXP asking you if you want it to do this automatically and it may have been off. I have Windows Vista now so I can't double check unfortunately.