Most PC users don't think much about the CMOS battery until their
computer shows signs of losing its BIOS settings on boot up. If you tend
to upgrade rather than replace your PC, replacing the CMOS battery
every couple of years makes sense.
Likewise, if you purchase a used PC, battery replacement is a good
idea unless the PC is less than two years old. It's just one more
preventive step you can take to prevent troubles in the future.
If you have never replaced a CMOS battery before, you can find step-by-step instructions below.
In most cases, frequent CMOS errors are a sign of a dead battery. The
CMOS battery maintains your settings while your PC is powered off. You
can easily replace the battery yourself.
- Boot your PC and enter its setup mode.
- Write down all of the settings from the various BIOS menus. Click this link to learn more about this procedure.
- Power off your PC.
Open the case of your computer
Figures 1-2. Undoing the screws on your PC case.
Figure 3. Opening the case of your PC.
Locate the battery on the motherboard.
Figure 4. Battery location on the motherboard.
The layouts of the components differ on different motherboards, so
you'll have to consult your motherboard user manual for specifications
about the battery and its location.
This is a close-up view of the battery on the motherboard.
Figure 5. Typical CMOS battery.
The most common type of batteries used in modern PCs is coin-shaped
lithium/manganese-dioxide battery that looks like a large watch
- Obtain a replacement battery from a local or online computer parts dealer.
Remove the old battery.
Figure 6. Removing the old battery.
Replace it with the new one, as shown on the picture below.
Figure 7. Replacing the battery.
- Document the date of replacement for future reference.
- Replace the case and power on the PC.
- Enter the setup mode of your PC.
- Reenter the settings you have written down from the various setup menus.
- Don't forget to observe proper anti-static precautions when working inside the case of your PC.
- If you can't see your battery right away, try removing expansion
cards or unplugging cables. The majority of newer motherboards use
lithium batteries that look like large watch batteries.
If the battery is already dead and you receive messages saying "CMOS checksum error", skip Step 1 and Step 2.