A CMOS battery, or complementary metal-oxide-semiconductor battery, is a small coin-shaped battery that powers the CMOS memory chip on a computer’s motherboard. The CMOS memory chip stores the computer’s BIOS settings, which include the time and date, hardware configuration, and other important system information. If the CMOS battery dies, the BIOS settings will be lost and the computer may not be able to boot properly.
CMOS batteries typically last for several years, but they can eventually die and need to be replaced. If you are experiencing problems with your computer’s time and date settings, or if you are getting error messages related to the CMOS memory, it is possible that the CMOS battery is dead and needs to be replaced.