The clock in your computer needs a battery to help keep the time when your computer is turned off.

This is normally called the CMOS battery. Inside your computer is a BIOS chip that keeps certain settings and includes a real time clock. The battery in most computers are normally a CR2032 which is approximately the size of a small coin. The battery will last from two to ten years depending on how long your computer is off, the ambient temperature will also have an effect on battery life.

The battery is used to keep the clock ticking and to keep the BIOS chip energised which in turn keeps your BIOS settings in place. When your battery runs flat, you lose your BIOS settings and the clock no longer functions. This can display "CMOS Checksum Error" on bootup and your computer may not operate properly.

It is quite an easy job to replace the battery, but setting up the BIOS can be tricky, so we would recommend having an engineer replace the battery and setup your BIOS correctly.