If it's the battery on the motherboard, usually there is a warning message of some kind, something like CPU fan failure. But it's not the fan, it has to do with the BIOS, which does have the timing. Upside is the battery is around $4 and usually easy to swap out, making sure to use the same number and orientation. Tho' Vista seems too new to have that problem.
But, flip side, you can click/open your time on the TaskManager, click the Internet Time, choose from the drop-down arrow for time.nist.gov, click the box for Auto synchronize with internet time server and click Apply. You may already have this set. Here again, I don't know if it's the same for Vista.