There are three computer battery types used with computers. First is the backup battery, which is commonly referred to as the CMOS battery that holds your computer’s settings, such as the time and date. Without a CMOS battery, you would have to reset the time, date, and other system settings each time the computer starts.

Second, the  is only found in portable computers as a temporary backup for the main battery. A bridge battery lets you remove the main battery and replace it with a good battery without having to turn off the computer.

Third, the main battery in portable computers is an alternate source of energy for when the computer is not connected to a wall outlet.