What is a CMOS battery, and why does my computer need one?

All personal computers require a small battery on the system board that provides power to the Complementary Metal Oxide Semiconductor (CMOS) chip, even while the computer is turned off. This chip contains information about the system configuration (e.g., hard disk type, floppy drive types, date and time, and the order in which the computer will look for bootable disks). The CMOS battery allows the CMOS to preserve these settings.

The purpose of the CMOS battery most often today is simply to allow your computer to remember what time it is. If the battery dies or removed then when your computer boots it will have forgotten the current date and time.

Most CMOS batteries will last the lifetime of a motherboard but will sometimes need to be replaced. Incorrect or slow system date and time and loss of BIOS setting are major signs of a dead or dying CMOS battery. When we are trying to change the CMOS battery for that we first have to know what model of CMOS battery you are using.