|So you put a voltmeter to the battery and it checked out at 3 volts (or close to it)?|
Is it the bios that's asking for that info? If so, are you saving the settings when you exit?
Or is it a white-on-black dos screen that shows after the OS starts to load?
And it is windows XP? There was a DATE and TIME command that could be loaded in autoexec.bat for dos and win 9x. If there, you'd be prompted to enter a value or just hit ENTER.
If that's what you seem to be experiencing then it may be in AUTOEXEC.NT, which is what XP uses. Here's some info on that file:
You're not really green until you're soylent green.