Your PC is made up of several systems that need to work together for everything to run smoothly. We're talking about things like memory timings, boot device priorities, and other low-level settings. This important information is stored in your system’s UEFI/BIOS.
But just like how your PC loses the contents of RAM when it powers down, your BIOS would lose its settings too. At least it would if it weren’t for a small battery on your motherboard. That battery is the CMOS (Complementary Metal-Oxide Semiconductor) battery. It’s a flat, coin-shaped device which explains why it’s often referred to as a coin cell battery. Its job is to keep your BIOS settings intact even when the PC is turned off.
Since it’s a non-rechargeable battery, it will eventually run out. When that happens, your PC might take longer to boot, forget your BIOS settings, or most noticeably, show the wrong date and time. That last one can cause all sorts of issues, so it’s worth fixing quickly.
How to Replace a CMOS Battery
The good news is that replacing a CMOS battery is easy. They’re inexpensive and widely available. Check your motherboard manual, but generally you’re looking for a CR2032 battery, which you can find in hardware stores, supermarkets, or online. Amazon sells a four-pack for around $4. Since these batteries can last up to 10 years, one pack should keep you covered for a while.
Here’s how to replace it:
1. Turn off your PC and unplug it. Open the side panel of your case.
2. Locate the CMOS battery. It’s a silver disc about 20mm across.
3. Remove the old battery. There’s usually a small clip holding it in place. Gently release it and the battery should pop out.
4. Insert the new battery. Make sure it’s the right way up (positive side facing out) and press it into place until it clicks.
That’s it. Power up your machine, enter the BIOS, and set the correct date and time. Set your memory timings using XMP or EXPO. Save your settings and you’re good to go.