Removing the CMOS battery takes five minutes and requires only a Phillips screwdriver and steady hands

The CMOS battery is a coin-shaped cell on your motherboard that keeps your BIOS settings and system clock running when the computer is powered off. Removing it is straightforward: power down completely, open the case, locate the battery (usually a silver disc near the center of the board), and pop it out of its socket. You do not need special tools or technical training. The battery sits in a plastic holder that releases with gentle upward pressure.

Most people remove the CMOS battery for one of two reasons: to reset the BIOS to factory defaults (useful if you have forgotten a password or made settings changes that prevent the computer from starting), or because the battery is dead and the system clock keeps resetting. Either way, the removal process is identical.

Key Takeaways

  • Power off the computer completely, unplug it, and wait at least 30 seconds before opening the case to let capacitors discharge.
  • The CMOS battery is a round, silver, coin-sized cell usually located near the center of the motherboard in a plastic clip holder.
  • Press the clip or holder gently upward to release the battery; it will pop out without force.
  • Removing the battery for 10 to 15 minutes clears BIOS settings and resets the system clock to a default date.
  • Reinstall the battery with the positive side (marked with a + symbol) facing upward, and the computer will resume normal operation.

Prepare the computer and workspace

Start by shutting down the operating system normally. Do not force a power-off. Once the system is fully off, unplug the power cable from the back of the case. This step is essential because it removes all electrical current from the motherboard.

Wait at least 30 seconds after unplugging. This allows the capacitors on the motherboard to discharge completely. Touching a live capacitor can cause a shock or damage components. After the wait, open the computer case. Most modern cases have two side panels held by thumbscrews or a few Phillips screws. Remove whichever panel gives you clear access to the motherboard. Set the screws in a small container so you do not lose them.

Ground yourself before touching the motherboard. Touch a metal part of the case frame with your bare hand, or wear an anti-static wrist strap clipped to the case. This prevents static electricity from your body from damaging sensitive components.

Locate the CMOS battery on the motherboard

The CMOS battery is a round, silver, metallic disc about the size of a US dime or slightly larger. It looks like a watch battery. On most motherboards, it sits in a plastic clip holder near the center of the board, often between the CPU socket and the edge of the board, or near the RAM slots.

If you cannot find it when ready, consult your motherboard manual. The manual will show a diagram with the battery location labeled. If you do not have the manual, search online for your motherboard model number (printed on the board itself) plus "CMOS battery location." Most manufacturers publish diagrams online.

The battery holder is usually white or black plastic with a small metal clip on one or both sides. The clip holds the battery in place. Some holders have a small lever or tab you can pull; others require you to press the clip itself.

Remove the battery from its holder

Look at the clip or holder closely. If there is a small lever or tab, pull it gently away from the battery. If the holder has a clip on the side, press the clip gently downward or outward, depending on its design. The battery will pop up slightly out of the holder as the clip releases.

Once the clip releases, use your fingernail or a plastic spoon handle to lift the battery straight up and out of the holder. Do not use a metal tool that could slip and scratch the motherboard. The battery comes out easily once the clip is released; if you feel strong resistance, stop and check that the clip is fully disengaged.

Set the battery aside on a clean, dry surface. Do not touch the battery contacts or the motherboard contacts with your fingers more than necessary, as oils from your skin can cause corrosion over time.

Wait before reinstalling or replacing the battery

If your goal is to reset the BIOS, leave the battery out for 10 to 15 minutes. This allows the motherboard capacitors to fully discharge, which clears all stored BIOS settings and resets the system clock. Some motherboards have a jumper on the board labeled "CLR_CMOS" or "PSWD" that does the same thing, but removing the battery is the most reliable method.

If you are replacing the battery because it is dead, you can install the new one when ready. CMOS batteries last five to ten years on average. If your system clock resets every time you power off, or if the BIOS shows an error message about the battery, the cell is likely exhausted.

Reinstall the battery or install a replacement

When you are ready to reinstall, check the battery for a + symbol on one side. This marks the positive terminal. The battery must go back into the holder with the + side facing upward, toward you. The holder is designed so the battery only fits one way, but it is worth checking before you press it in.

Place the battery into the holder and press down gently until the clip snaps back into place. You will hear or feel a small click. The battery should sit flush with the holder, not sticking up. If it does not sit flat, remove it and check that the + side is facing up.

Close the computer case and replace the screws or thumbscrews. Plug the power cable back in and power on the computer. The system should start normally. If you removed the battery to reset the BIOS, you may see a message during startup saying the CMOS battery is low or settings have been reset. This is normal. You can enter the BIOS setup (usually by pressing Delete, F2, or F12 during startup, depending on your motherboard) and reconfigure any settings you need.

What to do if the battery does not fit or the holder is damaged

If the battery holder is cracked or the clip is broken, the battery will not stay in place. In this case, you have two options: replace the holder itself (requires soldering and is not recommended for most users), or use a small piece of non-conductive tape to hold the battery in place temporarily while you source a replacement motherboard or take the computer to a technician.

If you install a new battery and it does not fit into the holder, check that you have the correct battery type. Most CMOS batteries are CR2032 cells, but some older motherboards use CR2025 or other sizes. The battery package will list the type. If you bought the wrong size, return it and get the correct one.

Frequently Asked Questions

Will removing the CMOS battery erase my hard drive or files?

No. The CMOS battery only powers the BIOS settings and the real-time clock. It does not affect your hard drive, SSD, or any files stored on them. Removing the battery resets only the BIOS to factory defaults and clears the system clock.

How long can I leave the CMOS battery out?

You can leave it out indefinitely. The longer it is out, the more completely the BIOS settings will clear. For a full reset, 10 to 15 minutes is sufficient. If you leave it out for hours or days, the result is the same.

What if my computer does not start after I reinstall the battery?

Check that the battery is fully seated in the holder and the clip is engaged. Power off, unplug, wait 30 seconds, and try again. If the computer still does not start, the battery may be installed upside down. Remove it, flip it so the + side faces up, and reinstall.

Can I touch the CMOS battery with my bare hands?

Yes, it is safe to handle the battery with your bare hands. Avoid touching the metal contacts on the motherboard itself, as oils from your skin can cause corrosion, but the battery itself is not damaged by skin contact.

How do I know if my CMOS battery is dead?

The most common sign is that your system clock resets to a default date (often 2000 or 2005) every time you power off and back on. You may also see a CMOS battery error message during startup. If either happens, the battery needs replacement.