When your personal computer is turned off, the motherboard depends on a standard three-volt battery to maintain the CMOS (Complementary Metal Oxide Semiconductor), or flash memory chip. The CMOS battery runs a small charge through the memory chip to retain your computer's important system settings, such as the BIOS (Basic Input Output System) startup information, as well as the current time and date.
Facts
Normally, the lifespan of a CMOS battery is about four to five years, but you should replace the battery every two or three years before it begins to fail. A failing CMOS battery will cause your computer to develop memory loss and other unusual symptoms. For instance, boot failure can occur due to unusual BIOS settings that have been wiped when your computer was turned off. Your computer may display incorrect times and dates in the BIOS or within your computer system.
If you have an older computer and it begins to develop memory loss, your system clock continuously resets itself or old settings disappear, you should not overlook this problem to avoid system failure.
Significance
A failing CMOS battery can easily be fixed by replacing it with a new one. It is essential that you replace the battery with the same type that is installed on your computer's motherboard.
Identification
You can purchase a circular-type CR-2032 three-volt lithium battery at most electronics stores and expect to pay about $3 or less for it. Never replace the CMOS battery with a rechargeable battery. A rechargeable battery will become unstable, burst or explode, causing damage to your computer's motherboard.
Function
A new CMOS battery will refresh the CMOS memory chip. The CMOS battery is usually mounted on the motherboard and can be removed with a thin screwdriver.
Once you have installed a new CMOS battery, restart your computer, and change the date in the BIOS setup to the current date. Shut your computer down, and unplug your computer's power cords for about 15 minutes. Plug the power cords back in, and restart your computer. Verify that the current date settings have not changed. If the current date is displayed, the CMOS battery is working properly, and your system should return to normal.
Warning
Before you open your computer case to replace the CMOS battery, take several precautions to keep yourself grounded. Unplug all power cords from their outlets, and wear an antistatic wrist strap. Work in a well-lit, static-free area, and avoid working in carpeted areas.
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