A CMOS battery is a small memory cell present on the motherboard of all desktop, laptop, netbook and PDA computers. It stores BIOS settings. The CMOS battery is important should the power go out or the rechargeable battery on your laptop, netbook or PDA die. The computer's pertinent information will be saved, thanks to the CMOS battery. If the CMOS battery is dead or has been removed, the computer will still work, but should the computer not receive power, whether it be from an electrical source or a battery source, all information stored on the computer and not backed up elsewhere can be lost.
Press the "Power" button to turn the computer on. Allow the system to boot up normally.
Click "Ok" when you receive a pop-up indicating the CMOS battery is not working. Common error messages include CMOS Read Error, CMOS checksum error or CMOS Battery Failure.
Press the "Power" button to shut off the computer when you are done working on the computer.