How to Replace the CMOS Battery

The majority of issues with a Windows or Linux PC can be resolved by tweaking the operating system, changing settings or (in the case of Windows) installing some updates. However, there is one particularly frustrating issue that can only be resolved by replacing a component.

If you’ve ever booted up your PC or laptop and discovered that the time has reset to January 1st, 1980, then the time has come to replace the CMOS battery. This small component is basically a wristwatch battery, and its purpose is pretty much identical – it lets your computer tell the time.

This is important for several reasons, not least because your computer needs to know the time when sending emails, logging onto remote file servers and even for scheduled tasks such as anti-virus scans and backups.

In the old days of computing, the CMOS battery also stored your BIOS settings. This is no longer the case, however, although you will need to reset the clock to the correct date and time after replacing the component.

How to Replace the CMOS Battery
Replacing the CMOS Battery

Depending on what type of computer you have, replacing the CMOS battery should be pretty straightforward. Note, however, that this isn’t always the case.

For desktops, replacing the component is easiest. All you need to do is unplug the computer, remove the side of the case to present access to the motherboard and, assuming you have taken the necessary anti-static precautions, using a small flat-edged screwdriver prize the battery from its compartment, usually found to the right of the PCI/PCI-e slots. You should insert a replacement battery straightaway and then replace the cover to continue booting your PC.

With laptops and netbooks, however, the problem is a little more complicated. The issue here is that there are so many different form factors and chassis types for laptops that even getting to the battery can be difficult, and this is before discovering that laptop motherboards differ wildly from manufacturer.

If you have to replace the CMOS battery on a laptop, take the same anti-static precautions as you would when opening a PC but spend some time on the web first of all looking into how your laptop can be opened and the battery found and replaced.
Reconfiguring Your CMOS Settings

Once the battery has been swapped with a new, fully charged replacement, you can then go about the task of setting the correct system time on your computer. There are two ways of doing this, either via the BIOS (typically entered by tapping the DEL key as your computer starts) or in the operating system.

Whichever method you choose, the new CMOS battery should retain the new time and date settings the next time the computer restarts. If this doesn’t happen, however, then you likely have a faulty battery or an issue with the motherboard, which will require further investigation and possibly even a replacement.