What a CMOS battery reset does and when you need one

A CMOS battery is a small coin-cell battery on your motherboard that keeps your computer's date, time, and BIOS settings alive when the machine is powered off. When that battery dies or loses charge, your computer forgets these settings and may fail to start properly. Resetting the CMOS battery clears all stored settings and returns them to factory defaults — this fixes boot problems, forgotten BIOS passwords, and incorrect date/time that won't update.

You do not need special tools or software. The process takes 10 to 15 minutes and involves opening your computer case, removing the battery for a short time, and putting it back. This is a physical fix, not a software one, and it works on desktop computers. Laptops rarely let you access the CMOS battery without professional disassembly.

Key Takeaways

  • Resetting the CMOS battery requires opening your computer case and physically removing a small coin-cell battery from the motherboard for 30 seconds to 5 minutes.
  • You must power off the computer completely, unplug it from the wall, and wait before opening the case to avoid electrical damage.
  • The battery slot is usually labeled on the motherboard; if you cannot find it, check your motherboard manual or search the model number online.
  • After reinserting the battery, your BIOS settings return to factory defaults, so you may need to adjust date, time, and boot order again.

Before you open the case: power down and ground yourself

Start by shutting down your computer normally through the operating system. Do not force a shutdown by holding the power button. Once the screen goes dark, wait 10 seconds, then press the power button again to make sure the system is fully off.

Unplug the power cable from the back of the computer. This step is critical — even when a computer appears off, the motherboard still carries a small electrical charge. Unplugging removes that charge and prevents damage to components or injury to you.

Before you touch anything inside the case, ground yourself by touching a metal part of the case frame or wearing an anti-static wrist strap. Static electricity can damage the motherboard. If you have an anti-static mat, place it on your work surface and stand on it while working inside the case.

Locating and removing the CMOS battery

Open your computer case. Most desktop cases have two or four thumbscrews on the back panel, or a latch on one side. Remove the side panel that gives you the clearest view of the motherboard. Set the screws somewhere you will not lose them.

Look for a small circular battery about the size of a coin — usually silver or gold in color. It sits in a round slot on the motherboard and is often labeled CMOS, BATT, or RTC. If you cannot spot it, consult your motherboard manual or search for your motherboard model number plus "CMOS battery location" online. Motherboard layouts vary widely, and the manual will show you exactly where it is.

Gently press down on the small metal clip or lever on one side of the battery slot. The battery will pop up slightly. Lift it out by the edge — do not touch the flat surfaces of the battery itself, as skin oils can interfere with the connection. Set the battery on a clean, dry surface nearby.

How long to leave the battery out

Leave the battery out for at least 30 seconds. This time allows the motherboard to fully discharge and forget all stored settings. Many people leave it out for 5 to 10 minutes to be certain, and this does no harm. There is no risk of leaving it out longer — the longer you wait, the more complete the reset.

While the battery is out, you can visually inspect the slot and the battery itself for dirt, corrosion, or damage. If the battery looks heavily corroded or the slot appears damaged, the battery may need replacement rather than reinsertion. A new CMOS battery costs between $5 and $15 and is widely available online or at electronics retailers.

Reinserting the battery and powering on

Pick up the battery by its edge and align it with the slot. The flat side with the label should face up. Press it down gently until it clicks into place and the metal clip or lever snaps back over it. The battery should sit flush with the slot — if it is sticking up or feels loose, remove it and try again.

Close the computer case and replace the side panel. Tighten the thumbscrews or latches securely, but do not overtighten — you are just holding the panel in place, not clamping it.

Plug the power cable back into the wall outlet and the computer. Press the power button. The computer should start normally. You may see a message on the first boot saying the CMOS settings have been reset or that the date and time are incorrect — this is normal and expected.

What to do after the reset is complete

Once the computer boots, enter the BIOS setup. The key to press is usually Delete, F2, or F12 — the screen often shows which key to press during startup. Check the date and time, and correct them if needed. Adjust any other settings you changed before the reset, such as boot order or hardware settings.

If you had a BIOS password set, it is now gone. You can set a new one if you want to protect your BIOS settings from unauthorized changes. Save your changes and exit the BIOS. The computer will restart and load your operating system normally.

If the computer still will not start after the reset, the problem may not be the CMOS battery. Check that the power cable is firmly connected, that the case is fully closed, and that no cables inside the case have come loose during your work. If the issue persists, the motherboard itself may be faulty.

When a CMOS battery reset will not fix your problem

A CMOS reset solves boot failures caused by corrupted BIOS settings, forgotten passwords, and incorrect date/time. It does not fix hardware failures, driver problems, or operating system errors. If your computer shows error messages about hard drives, RAM, or other components, those parts may be failing and need replacement or repair.

If your computer boots but runs slowly, crashes, or shows blue screens, the CMOS battery is not the cause. Those symptoms point to software issues, malware, failing storage drives, or overheating — none of which a CMOS reset will address. A CMOS reset is a last resort for boot problems, not a general troubleshooting step.

Frequently Asked Questions

Can I reset the CMOS without opening the case?

No. The CMOS battery is a physical component on the motherboard, and you must remove it to reset the settings. Some older computers have a jumper on the motherboard that can reset CMOS without removing the battery, but this is rare on modern boards. Check your motherboard manual to see if yours has this feature.

What if I cannot find the CMOS battery?

Search your motherboard model number plus "CMOS battery" on the manufacturer's website or a search engine. The manual will show you the exact location. If your motherboard is very old or custom-built, you may need to contact the manufacturer directly. Do not guess — removing the wrong component can damage your computer.

How do I know if my CMOS battery is dead?

Signs include the computer forgetting the date and time every time you restart, BIOS settings reverting to defaults, or the computer failing to boot with an error message about CMOS. If you see these symptoms, the battery is likely dead and should be replaced after the reset.

Is it safe to touch the CMOS battery with bare hands?

It is safe, but not ideal. Skin oils can corrode the battery contacts over time. Wear latex gloves or hold the battery by its edge to minimize contact with the flat surfaces. If you have already touched it, do not worry — one or two touches will not cause when ready problems.

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

Not necessarily. If the battery is straightforward discharged, reinserting it allows it to recharge. If the battery is old or corroded, replacement is a good idea — a new battery costs little and lasts 5 to 10 years. If the computer forgets settings again within days of the reset, the battery is likely dead and needs replacement.