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Your CMOS Battery
General Misc.

When was the last time you thought about the battery in your PC? The battery that protects your valuable CMOS data when your desktop isn't powered on.

Most recent motherboards come with coin shaped lithium/manganese-dioxide batteries that look like large watch batteries. These batteries are advertised to have a life span of five years. That's longer than many people keep their PCs!

When should you replace your battery?

Even though the lifespan of the battery might be five years under the best of circumstances, don't wait until the battery dies to replace it. Remember that the battery is the only thing standing between you and the loss of your CMOS settings when you power down your PC.

If you keep your PC long term without swapping out the motherboard, you should consider changing the battery every two to three years. Why change the battery sooner? Simply this. If you wait until the battery begins to die, your PC can forget its CMOS settings.

Symptoms of a dying batter.
Often, a dying battery will first manifest itself intermittently. Sometimes, you will boot with no problem. At other times, you will see an error indicating that the system doesn't match the configuration. When the battery fails entirely, the message will either come up every time you reboot, or your BIOS may report an error number with a message stating that the battery is dead.

Protecting your CMOS settings

When you replace your battery, the CMOS settings will immediately be lost. In addition, battery corrosion (more common in older PCs) or other battery problems may cause the battery to die more suddenly than its expected lifetime. For this reason, it is important to keep a record of your CMOS settings.

A paper record of your CMOS setup is always a good thing to have.

Many utility suites, such as Norton Utilities, will allow you to create a floppy disk backup of your settings. This can be extremely handy for battery problems as well as recovering from other CMOS errors.


Most PC users don't think much about the CMOS battery until their computer shows signs of losing its settings on boot up. If you tend to upgrade rather than replace your PC, replacing the CMOS battery every couple of years makes good sense.

Iif you purchase a used PC, a battery replacement is a good idea unless the PC is significantly less than two years old. It's just one more preventive step you can take to prevent trouble down the road.

Never replaced a CMOS battery before? Click

This excellent tip courtesy of CNET

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