What a CMOS Battery Does and Why You Might Remove It
The CMOS battery is a small coin-shaped battery on your computer's motherboard that keeps your BIOS settings and system clock running even when the computer is unplugged. Removing it is one of the fastest ways to reset your BIOS to factory defaults — useful if you've locked yourself out of BIOS settings, forgotten a BIOS password, or need to troubleshoot boot problems. The battery itself rarely fails, but removing and reinserting it can solve certain hardware issues.
This is a straightforward task that takes about five minutes and requires no special tools beyond a Phillips screwdriver and your hands. The battery sits in a small clip on the motherboard and pops out easily once you locate it.
Key Takeaways
- Power down your computer completely and unplug it from the wall before opening the case, then wait at least 30 seconds to let residual power drain.
- The CMOS battery looks like a flat silver coin (usually CR2032) and sits in a spring-loaded clip somewhere on the motherboard — check your motherboard manual if you cannot find it.
- Press the small metal clip holding the battery toward the center of the battery, and it will pop out; you do not need to force it.
- Leave the battery out for at least 10 to 15 minutes so the BIOS fully resets, then reinsert it the same way it came out.
Preparing Your Computer for Safe Battery Removal
Start by shutting down your computer completely — not sleep mode, but a full shutdown. Close all programs, click the power button, and wait for the screen to go black and all lights to stop.
Unplug the power cable from the back of the computer tower. This step is critical because even when a computer is off, electricity still flows through the motherboard. Unplugging removes that power entirely. Wait at least 30 seconds after unplugging before you open the case — this gives any residual electrical charge time to drain.
Open your computer case by removing the side panel. Most cases have two or three thumbscrews on the back, or a latch you slide. Lay the case flat on a clean, dry surface so you can see the motherboard clearly. If you are working on a laptop, the process is similar but you may need to remove the keyboard or bottom panel first — check your laptop's manual for the exact location of the CMOS battery.
Locating the CMOS Battery on Your Motherboard
The CMOS battery is a small, flat, round battery that looks like a large coin — usually silver or gray. The most common type is a CR2032 battery, about the size of a dime but thicker. It sits in a small plastic clip that holds it in place, and the clip is mounted directly on the motherboard.
The battery's location varies by motherboard model. On most desktop motherboards, it sits somewhere in the lower half of the board, often near the edge or between the RAM slots. On some boards it is near the BIOS chip (a larger rectangular chip with a label). If you cannot spot it after a quick look, consult your motherboard's manual — the manual will have a diagram showing exactly where the CMOS battery is located. You can usually find the manual online by searching for your motherboard model number.
If you are working on a laptop, the CMOS battery is typically smaller and may be soldered directly to the motherboard or held in a clip similar to a desktop board. Laptop manuals are especially important here because the battery's location and removal method vary widely.
Removing the Battery from Its Clip
Once you have located the battery, look at the small metal clip holding it in place. The clip has a tiny arm or tab that you will press to release the battery. This tab is usually on one side of the clip and points toward the center of the battery.
Using your fingernail or a plastic tool (not a metal screwdriver, which could damage the board), gently press the metal clip tab toward the center of the battery. Do not force it — the clip is designed to release smoothly. As you press, the battery will pop up slightly out of the clip. Once it lifts, you can slide it out with your fingers or gently pry it free with a plastic tool.
If the battery does not pop out easily, stop and look again at the clip. Make sure you are pressing the correct tab. Some clips have the release tab on the opposite side from where you might expect. If you are still stuck, take a photo of the battery and clip, then search online for your specific motherboard model — someone has likely posted a photo or video showing the exact removal method.
Waiting for the BIOS to Reset
Once the battery is out, leave it removed for at least 10 to 15 minutes. During this time, the CMOS memory — which stores your BIOS settings — loses power and clears completely. This is what resets your BIOS to its factory defaults. Some people wait longer (up to 30 minutes) to be absolutely certain, but 10 to 15 minutes is usually enough.
While you wait, do not plug the computer back in or close the case. Just let it sit with the battery out. This is a good time to check that you have not accidentally knocked any cables loose or disturbed any other components inside the case.
Reinserting the Battery and Powering On
After the waiting period, pick up the CMOS battery and look at it. You will see a plus sign (+) or minus sign (−) printed on one side — this indicates the polarity. The side with the plus sign should face up (toward you) when you reinsert it into the clip.
Slide the battery back into the clip the same way it came out, making sure the positive side faces up. You should hear or feel a small click as the clip snaps back into place and holds the battery. The battery should sit flat and flush in the clip, not tilted or sticking out.
Close your computer case, plug the power cable back in, and power on the computer. Your BIOS has now been reset to factory defaults. You may see a message on startup saying the CMOS battery was removed or that BIOS settings have been reset — this is normal. Your computer should boot normally. If you had a BIOS password set, it is now cleared and you can enter BIOS setup without a password.
What to Do If Something Goes Wrong
If your computer does not power on after reinserting the battery, first check that you have plugged the power cable back in firmly. Then open the case again and make sure the battery is seated correctly in its clip and the positive side is facing up.
If the computer still does not start, check that you did not accidentally disconnect any cables inside the case when you were working. The most common cables to accidentally bump are the power connectors to the motherboard — look for thick cables with multiple pins plugged into the board. If a cable is loose, reseat it firmly.
If you are still having trouble after these checks, the issue may not be related to the CMOS battery. Try leaving the battery out for a full 30 minutes instead of 10 to 15, then reinsert it and try again. If the computer still will not start, you may need to consult your motherboard manual or contact the manufacturer for support.
Frequently Asked Questions
How long does a CMOS battery last?
A CMOS battery typically lasts three to ten years depending on how often your computer is powered on and off. If your computer is always plugged in and running, the battery lasts longer. If you notice your system clock keeps resetting to the wrong time after you power off the computer, the battery may be wearing out and will need replacement.
Can I damage the motherboard by removing the CMOS battery?
No, removing the CMOS battery is safe as long as the computer is unplugged and you wait 30 seconds before opening the case. The battery is designed to be removed and reinserted. Just avoid touching other components on the motherboard and be careful not to knock any cables loose.
Will removing the CMOS battery erase my files or programs?
No. The CMOS battery only stores BIOS settings and the system clock — it does not store your files, programs, or operating system. Removing it will not affect anything on your hard drive or solid-state drive. Your files and programs will be exactly as you left them.
What if I cannot find the CMOS battery on my motherboard?
Check your motherboard manual first — it will have a diagram showing the exact location. If you do not have the manual, search online for your motherboard model number plus "CMOS battery location." If your motherboard is very old or very new, the battery location may be unusual or the battery may be soldered directly to the board, in which case you may need professional help to remove it.
Do I need to replace the CMOS battery after I remove it?
Not necessarily. If you removed it to reset your BIOS, you can straightforward reinsert the same battery. If the battery is old and your system clock keeps resetting, you can buy a replacement CR2032 battery at any pharmacy or electronics store for a few dollars and swap it in the same way.