The complementary metal-oxide semiconductor, or CMOS, chip is a motherboard component that stores the basic input/output system, or BIOS, settings of the computer. It comes with its own battery power to retain stored information regardless of the power state of the computer.
In most cases, the CMOS battery works up to 10 years before needing a replacement. The CMOS chip loses all custom settings stored in it when it loses power. A user can usually suspect the CMOS battery is dying when the computer keeps showing a wrong system date and time and the BIOS setting keeps resetting to the default options every time the computer boots. Regardless of its battery level, a user can also revert the CMOS chip to its factory settings through the BIOS utility software.