One of the steps in our refurbishing process at The Working Centre's Computer Recycling Project involves testing the CMOS battery inside each desktop PC we refurbish. Testing the CMOS battery is a relatively simple process and you can do it a number of ways. The simplest is with a cheap battery tester. You can sometimes find these at dollar or hardware stores. But battery testers can't be found everywhere so the next simplest method is with a multimeter.