Redemption, your comment about desktop CMOS battery is a couple of weeks old so not sure this still applies, but those batteries are easy to find and replace. They're all the same and are dime-sized batteries equivalent to CR2032 and 3V. They can be found at places like Canada Computers and usually found near the cash register exits. They're inexpensive at roughtly a couple of $ if I remember correcly.
If you do replace it, you will need to go into the BIOS settings and re-set date, time and any other specific settings you might have had in the bios since everything will go back to default after change.