What clearing the CMOS battery does

Clearing the CMOS battery resets your computer's BIOS settings to factory defaults. The CMOS battery is a small coin-shaped battery on your motherboard that keeps your BIOS settings and system clock running even when the computer is powered off. When you clear it, you erase any custom settings you've made in the BIOS menu — things like boot order, overclocking adjustments, or password protections — and restore the computer to how it came from the manufacturer.

Most people clear the CMOS battery when they've forgotten a BIOS password, when the system clock keeps resetting, or when they want to troubleshoot a computer that won't start. It's a safe operation that doesn't affect your files, programs, or the operating system itself.

Key Takeaways

  • Clearing the CMOS battery resets BIOS settings to factory defaults but does not erase files or programs on your hard drive.
  • You can clear the CMOS by removing the battery for 10 to 30 seconds, using a jumper on the motherboard, or accessing a CMOS reset option in the BIOS menu itself.
  • Before you open the computer case, shut it down completely, unplug the power cable, and wait a few minutes for residual electricity to drain.
  • After clearing the CMOS, you will need to reset the system date and time and reconfigure any custom BIOS settings you had previously made.

Prepare your computer safely

Before you touch anything inside the case, shut down your computer completely and unplug the power cable from the wall outlet. Wait at least two to three minutes — this allows residual electrical charge to drain from the motherboard. Even with the power off, electricity can remain in the system and damage components or injure you.

If your computer is a laptop, you may also need to remove the battery (if it's removable) or hold the power button for 30 seconds to fully discharge the system. Desktops are generally easier to work with because the case opens more readily and the CMOS battery is more accessible.

Ground yourself before opening the case by touching a metal part of the case itself or wearing an anti-static wrist strap. This prevents static electricity from your body from damaging the motherboard.

Remove and reseat the CMOS battery

Open your computer case according to the manufacturer's instructions — usually this means removing one or two side panels held by screws or latches. Locate the CMOS battery on the motherboard. It's a round, silver, coin-shaped battery about the size of a dime, typically labeled CR2032 or similar. You'll usually find it near the edge of the motherboard or close to the BIOS chip.

Gently pry the battery out of its socket using a plastic spoon, plastic lever, or a non-conductive tool. Do not use a metal screwdriver directly on the battery, as metal can create a short circuit. Once the battery is out, wait 10 to 30 seconds. This time allows the CMOS memory to fully discharge. Then press the battery back into the socket until it clicks into place. The positive side (marked with a +) should face upward.

If you cannot easily remove the battery, check your motherboard manual — some boards have a jumper pin next to the battery that you can move to clear the CMOS instead. Moving the jumper to the "clear" position for 10 seconds, then moving it back, accomplishes the same reset without removing the battery.

Use the BIOS menu to clear CMOS

Some newer computers allow you to clear the CMOS directly from the BIOS menu without opening the case. Restart your computer and enter the BIOS setup by pressing a key during startup — commonly Delete, F2, F10, or F12, depending on the manufacturer. Your screen will usually display which key to press during the boot sequence.

Once in the BIOS menu, look for an option labeled "Reset to Defaults," "Load Defaults," "Clear CMOS," or "Factory Reset." The exact name and location vary by manufacturer. Select this option and confirm. The system will reset and restart automatically. This method is safest because you don't need to open the case or handle components.

Reassemble and reconfigure after clearing

Close your computer case and reconnect the power cable. Power on the computer and allow it to boot normally. You will likely see a message saying the CMOS has been cleared or that the system detected a configuration change. This is normal.

Once the operating system loads, open the BIOS menu again and reset the system date and time, which will have reverted to a default (often January 1, 2000, or the manufacturer's default date). If you had custom BIOS settings — such as a specific boot order, RAM timing, or overclocking adjustments — you will need to reconfigure them now. Write down any settings you remember before you clear the CMOS, or consult your motherboard manual for the recommended settings.

If you had a BIOS password set, it will now be cleared and you will be able to enter the BIOS menu freely. If you want to set a new password, you can do so in the BIOS security settings.

When to call a professional

If your computer still won't start after clearing the CMOS, the problem likely isn't the BIOS settings — it may be a failing hard drive, a power supply issue, or a hardware failure. Stop troubleshooting and contact a repair technician or the manufacturer's support line.

If you're uncomfortable opening your computer case, or if your computer is still under warranty, take it to a repair shop instead. Clearing the CMOS is straightforward, but opening the case carries a small risk of static damage if you're not careful, and some manufacturers void warranties if you open the case yourself.

Frequently Asked Questions

Will clearing the CMOS delete my files or programs?

No. The CMOS battery only stores BIOS settings and the system clock. Your files, programs, and operating system are stored on your hard drive and are not affected by clearing the CMOS.

How long should I wait after removing the CMOS battery?

Wait at least 10 to 30 seconds. Some sources recommend up to a minute to be certain the CMOS memory is fully discharged, but 10 to 30 seconds is usually sufficient.

What if I can't find the CMOS battery in my computer?

Consult your motherboard manual or search online for your specific motherboard model. The manual will show you exactly where the battery is located and may also describe an alternative method, such as a jumper pin or BIOS menu option, to clear the CMOS.

Do I need to replace the CMOS battery after clearing it?

No. Clearing the CMOS does not damage or drain the battery. The battery will continue to work normally. You only need to replace the battery if it fails — which you'll notice because your system clock resets every time you power off the computer.

Can I clear the CMOS while the computer is in sleep mode?

No. Always shut down the computer completely and unplug the power cable before opening the case. Sleep mode does not fully power down the motherboard, and electricity can still be present in the system.