A CMOS battery, or complementary metal-oxide-semiconductor battery, is a small, coin-shaped battery that is used to power the CMOS chip in a computer’s motherboard. The CMOS chip stores the computer’s BIOS settings, which include the date and time, hardware configuration, and other important information. If the CMOS battery dies, the BIOS settings will be lost and the computer will not be able to boot.
It is important to check the CMOS battery regularly to make sure that it is still working properly. A dead CMOS battery can cause a number of problems, including: