The memory and real-time clock are generally powered by a CR2032 lithium coin cell. These cells last two to ten years, depending on the type of motherboard, ambient temperature and the time that the system is powered off, while other common cell types can last significantly longer or shorter periods, such as the CR2016 which will generally last about 40% as long. Higher temperatures and longer power-off time will shorten cell life. When replacing the cell, the system time and CMOS BIOS settings may revert to default values. This may be avoided by replacing the cell with the power supply master switch on. On ATX motherboards, this will supply 3V standby power to the motherboard even if it is apparently "switched off", and keep the CMOS memory energised.
Some computer designs have used non-button cell batteries, such as the cylindrical "1/2 AA" used in the Power Mac G4 as well as some older IBM PC compatibles, or a 3-cell NiCd CMOS battery that looks like a "barrel" (common in Amigas and older IBM PC compatibles), which serves the same purpose.
Some computer designs have used non-button cell batteries, such as the cylindrical "1/2 AA" used in the Power Mac G4 as well as some older IBM PC compatibles, or a 3-cell NiCd CMOS battery that looks like a "barrel" (common in Amigas and older IBM PC compatibles), which serves the same purpose.
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