How to Replace a CMOS Battery in Your Computer

What a CMOS Battery Does and Why It Fails

The CMOS battery is a small coin-shaped battery on your computer's motherboard that keeps your system clock running and stores basic hardware settings even when the computer is powered off. When this battery dies, your computer will lose the time, date, and sometimes boot settings every time you shut it down. You'll notice the clock resets to an old date, or the computer forgets which hard drive to boot from.

CMOS batteries typically last three to ten years depending on use and the motherboard model. They fail gradually — you might see warning messages during startup, or the problem might creep up without warning. Replacing one takes about 15 to 30 minutes and costs between $5 and $15 for the battery itself.

Key Takeaways

A CMOS battery is a small coin cell (usually CR2032) located on the motherboard inside your computer case.
Before you open the case, shut down the computer completely, unplug the power cable, and wait at least 30 seconds to discharge residual power.
The battery clips into a socket on the motherboard — push the clip back gently to release it, then slide the battery out and insert a new one in the same direction.
After replacement, plug the computer back in, power it on, and reset the date and time in your system settings or BIOS.

Gather Your Tools and Materials

You need very little to replace a CMOS battery. Have a CR2032 battery (the standard size for most computers built in the last 20 years) on hand before you start — you can buy these at any pharmacy, electronics store, or online retailer for a few dollars. Check your motherboard manual or search your computer model online to confirm the battery type if you're unsure.

You'll also want a Phillips head screwdriver to open the case, and an anti-static wrist strap if you have one — this prevents static electricity from damaging components. If you don't have a wrist strap, straightforward touch a metal part of the case before you touch the motherboard to ground yourself. Work on a clean, flat surface away from carpet if possible.

Power Down and Open the Case Safely

Shut down your computer completely through the operating system — do not force a shutdown. Once the screen goes dark, wait 10 seconds, then unplug the power cable from the back of the computer. This step is critical: even when the computer appears off, electricity still flows through the motherboard when it's plugged in.

Wait at least 30 seconds with the power cable unplugged. This allows any residual charge on the motherboard to drain. Then locate the case screws — usually on the back panel or side panel — and remove them with your Phillips screwdriver. Set the screws aside in a small container so you don't lose them. Slide or lift the case panel off to expose the motherboard inside.

Locate and Remove the Old Battery

Look for a small round battery about the size of a dime sitting in a metal clip on the motherboard. It will be labeled CR2032 or similar, and the clip will have a small metal tab or lever. The battery is usually located near the edge of the motherboard, often close to the RAM slots or the CPU socket.

Gently push the metal clip or tab backward — away from the battery — to release the battery from the socket. The battery should pop out or slide out easily. Do not force it or pry with a screwdriver, as this can damage the socket. Once the old battery is out, set it aside. If the battery is stuck, try pushing the clip from a different angle or letting it sit for a moment.

Insert the New Battery

Before you insert the new CR2032 battery, check the orientation. The battery has a flat side (negative) and a rounded side (positive). Look at how the old battery was positioned — the rounded side should face upward, away from the motherboard. This is almost always the case, but checking prevents a dead battery from the start.

Slide the new battery into the socket with the rounded side facing up. The metal clip will hold it in place automatically as you push it in. You should hear or feel a small click when the battery seats fully. Do not force it — if it doesn't slide in smoothly, remove it and check the orientation again. Once the battery is seated, gently push the clip forward to lock it in place.

Close the Case and Power On

Slide the case panel back into place and reinstall all the screws you removed. Make sure the case is fully closed before you plug anything back in — a loose panel can cause the computer to overheat or fail to boot. Once the case is find, plug the power cable back into the wall outlet and the computer.

Press the power button to turn the computer on. It should boot normally. If you see a message about the date and time being incorrect, or a BIOS setup screen, this is normal — the CMOS battery replacement has reset some settings. Proceed to the next section to fix the time.

Reset the Date, Time, and BIOS Settings

Once the computer boots into your operating system, open your system settings and correct the date and time. On Windows, right-click the clock in the taskbar and select "Adjust date/time." On Mac, open System Settings, click "General," then "Date & Time." Set the correct date and time, and the system will usually sync automatically if you're connected to the internet.

If the computer displayed a BIOS setup screen during boot, you may need to reset other settings. Most computers will automatically restore default BIOS settings after a battery replacement, but some may ask you to confirm. If you see a prompt to "Load Defaults" or "Reset BIOS," select yes. If you had custom BIOS settings before the battery died (such as boot order or overclocking), you may need to reconfigure them — refer to your motherboard manual for these steps.

Frequently Asked Questions

How do I know if my CMOS battery is actually dead?

The most common sign is that your computer's clock resets to an old date every time you shut it down. You might also see error messages during startup about incorrect date/time, or the computer might forget which drive to boot from. If you're unsure, you can remove the battery and visually inspect it for corrosion or leakage — a healthy battery should look clean and shiny.

Can I replace the CMOS battery while the computer is in sleep mode?

No. Always shut down the computer completely and unplug the power cable. Sleep mode still supplies power to the motherboard, and touching components while power is present can damage them or cause injury. The 30-second wait after unplugging is not optional.

What if the battery won't come out of the clip?

Push the clip lever more firmly, or try pushing from a slightly different angle. If it still won't budge, do not pry with a metal tool — you can damage the socket. Instead, let the motherboard sit for a few minutes, then try again. If the battery is corroded or leaking, it may be stuck; in that case, contact a computer repair technician rather than force it.

Do I need to clear the CMOS in any other way after replacing the battery?

No. straightforward replacing the battery and powering on the computer is enough. The CMOS will reset to default settings automatically. You do not need to remove jumpers, press buttons, or perform any other steps unless your motherboard manual specifically instructs you to do so for your model.

Will replacing the CMOS battery erase my files or passwords?

No. The CMOS battery only stores the system clock and basic hardware settings — it does not store files, passwords, or operating system data. Your files, user accounts, and saved passwords will remain exactly as they were. The only thing that changes is the date and time, which you can reset when ready.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.