CMOS stands for “Complementary Metal Oxide Semiconductor.” The CMOS battery powers the BIOS firmware in your laptop [2]. BIOS needs to remain operational even when your computer isn't plugged into a power source. ... When your computer gets unplugged, BIOS relies on the CMOS battery for power.

What happens if CMOS battery is bad?

Removing the CMOS battery will allow your computer to run however, you will lose the date and time settings, the computer will boot with default BIOS settings or you will have to choose the drive that the OS is installed every time you start your computer.

What is the purpose of CMOS?

CMOS (short for complementary metal-oxide-semiconductor) is the term usually used to describe the small amount of memory on a computer motherboard that stores the BIOS settings. Some of these BIOS settings include the system time and date, as well as hardware settings.