Your CMOS battery is an essential part of your computer because it keeps enough power in the computer so it will remember such important settings as boot options and memory peripherals. It is vital to have this battery working inside your computer, so making sure it is in good health is important. While there isn't an actual test, keep an eye out for signs the CMOS battery is going out.
Is my CMOS battery bad?
There are settings you take for granted when your computer boots. These include your date/time settings, and the computer automatically booting your operating system drive and installed PCI slots on your computer. These are all controlled by the CMOS battery keeping a small charge inside of the computer to keep the memory alive enough to remember them. If there is no charge from the CMOS battery, or little charge even, you will notice your clock set to 12:00 and the date to Jan. 1 every time you start your computer. Your computer will also ask you where it should boot from when you turn it on. These are the most basic signs your CMOS battery is going dead and will be your ultimate test of the battery.
Computers usually do pretty well at self-maintenance, and this case is no different. If the CMOS battery is dying or dead, the computer will add a note to your boot screen that the CMOS battery lacks power and must be replaced. Because many CMOS batteries are now programmed into a motherboard, if any of these symptoms occur, you will more than likely need a replacement motherboard.
With older PCs, this is a problem after about five years. However, it should not be a problem for newer machines. New technology allows for these batteries to last as long as necessary, and if a CMOS battery goes dead, manufacturers consider this a defect. You should consult the manufacturer to check your eligibility for a replacement.