The word CMOS is an acronym for “complementary metal oxide semiconductor”. The CMOS battery is a small, round battery that lets you store the day, time, and month on your computer. It allows you to shut your PC down for an extended period of time and still have the correct time and date in place when you use your PC again. More importantly, the CMOS battery stores the BIOS settings of your computer. The BIOS enables us to identify what hardware is on the system and what device drivers to use. When the CMOS battery is weak, the BIOS loses data and the computer can start to malfunction. Let’s take a look at a few signs of a CMOS battery failure.