CMOS Battery

This article talks about 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.

Typical CMOS Battery

While the life span of the battery might be five years under ideal circumstances, it's not advised to wait until the battery is dead to replace it. Remember that the battery is the only thing that keeps you from losing CMOS settings when you power down your PC.

If you do not replace the motherboard on PC for a long time, you should consider changing the battery every two or three years. Why change the battery so soon? The reason is simple - if you wait until the battery begins to die, your PC can forget its CMOS settings.

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.

If you have a voltage meter, you can check whether or not the battery is healthy by measuring the voltage between the battery terminals that connect to the motherboard. The voltage should be higher than 2.5 volts. If the voltage reading is lower, you should change the battery right away.

Protecting your CMOS settings

When you replace the 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 sooner than its expected lifetime is over. 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 very useful when you encounter battery problems or when you are recovering from other CMOS errors.