The CMOS battery is a small coin-cell battery on your motherboard, usually located near the bottom edge or in a corner of the board

The CMOS battery powers the real-time clock and BIOS settings on your computer when the machine is off. Without it, your system loses the date, time, and hardware configuration each time you shut down. Finding it means opening your computer case and looking at the motherboard itself — the large circuit board that holds your CPU and RAM.

The battery is almost always a CR2032, a flat silver disc about the size of a dime, sitting in a small plastic holder clipped to the motherboard. It is not soldered down; it slides in and out by hand. The exact location varies by motherboard model, but it is never hidden under other components — manufacturers place it where you can reach it without removing the CPU cooler or RAM.

Key Takeaways

  • The CMOS battery is a removable CR2032 coin cell, silver and flat, sitting in a clip-style holder on the motherboard.
  • It is usually found along the bottom edge of the motherboard or in the lower corners, always in plain sight.
  • You can replace it by powering off the computer, opening the case, and sliding the old battery out and a new one in — no tools required.
  • If your computer keeps losing the date and time after shutdown, or forgets BIOS settings, the CMOS battery is likely dead.

How to locate the CMOS battery in your case

Start by shutting down your computer completely and unplugging the power cable. Wait 30 seconds, then open the case — most modern cases have a side panel held by two or three thumbscrews. Once inside, look at the motherboard. The CMOS battery will be a round, shiny silver disc, usually no more than half an inch across.

Scan the bottom third of the motherboard first, especially the corners and edges. It sits in a plastic holder that looks like a small cup with a clip on one side. If you cannot spot it when ready, consult your motherboard manual — search the model number (printed on the board itself) plus "CMOS battery location" online. The manual will show you a diagram with the exact spot marked.

Do not confuse the CMOS battery with other components. The battery holder is always separate and always accessible without removing anything else. If you see a battery that is soldered to the board or buried under cables, you are looking at something else.

Common locations by motherboard type

Desktop motherboards almost always place the CMOS battery along the bottom edge, either near the front panel connectors or near the PCIe slots. Laptop motherboards vary more widely — some put it near the edge of the board, others near the center, depending on the design. Older boards (pre-2010) sometimes placed it in the upper corners.

Server and workstation boards often use the same CR2032 in the same style of holder, but may position it differently to avoid interference with large coolers or expansion cards. If you are working on an older or unusual board, the manual is your fastest route to the answer.

How to remove and replace the battery

Once you have located the battery holder, look at the clip. It usually has a small tab or lever on one side. Push or slide that tab away from the battery, and the clip will spring open slightly. The battery will pop out or slide out easily — it is not glued or soldered. Drop the old battery aside.

Before inserting the new CR2032, check the orientation. The side marked with a plus sign (+) should face up, toward you. Slide the new battery into the holder, then press the clip back down until it clicks. The battery should sit flush in the holder with the clip holding it snugly in place.

Close your computer case, plug in the power cable, and turn the machine on. Your BIOS settings and the system date and time should now be preserved when you shut down. If the problem persists, the issue may be elsewhere — a failing power supply or a motherboard defect — rather than the battery itself.

Signs your CMOS battery is failing

The most obvious sign is that your computer forgets the date and time every time you power it off. You will boot up and see the clock reset to a default date, often January 1, 2000 or the year the motherboard was manufactured. This happens because the CMOS battery is too weak to hold the clock running during shutdown.

A second sign is that BIOS settings revert to defaults. If you have changed boot order, disabled certain hardware, or adjusted fan speeds in BIOS, and those changes disappear after a restart, the CMOS battery may be losing power. Some boards will also show a warning message during startup — "CMOS battery low" or "CMOS checksum error" — which is a direct signal that replacement is needed.

A dead CMOS battery does not prevent your computer from running. It only affects the clock and stored settings. If your machine boots and works normally but loses the date, the battery is almost certainly the culprit.

What to do if you cannot find the battery

If you have looked at the motherboard and cannot locate the CMOS battery holder, check the motherboard manual first. Search the model number (usually printed in small text on the board) and the word "manual" — most manufacturers publish PDFs online for free. The manual will have a diagram showing the exact location.

If the manual does not help or you cannot find it, take a photo of your motherboard and post it to a computer hardware forum like Tom's Hardware or your motherboard manufacturer's support community. Include the motherboard model number and a clear photo of both sides of the board. Someone familiar with that model can point you to the battery in minutes.

Some very old boards or specialized industrial boards may use a different battery type or a non-removable design. If you have confirmed the battery location and it looks soldered or permanently attached, do not attempt to remove it — contact the manufacturer or a repair shop instead.

Frequently Asked Questions

Can I replace the CMOS battery while the computer is on?

No. Always power off the computer completely and unplug the power cable before opening the case. Even with the machine off, the motherboard may retain a small charge. Waiting 30 seconds after unplugging gives that charge time to drain, reducing the risk of accidental damage to the board.

What type of battery do I need to buy?

Almost all desktop and laptop motherboards use a CR2032 battery. It is a standard coin cell sold at any pharmacy, supermarket, or electronics store for a few dollars. Check your motherboard manual to confirm, but CR2032 is the default for 99 percent of computers made in the last 20 years.

How long does a CMOS battery last?

A CR2032 typically lasts 3 to 10 years, depending on how often the computer is powered on and off. Computers that run constantly drain the battery faster than machines that are shut down daily. Once it fails, replacement takes less than five minutes.

Will replacing the CMOS battery erase my files?

No. The CMOS battery only stores the system clock and BIOS settings, not your documents, photos, or programs. Replacing it will not affect any files on your hard drive or SSD. Your data is safe.

What if the date and time still reset after I replace the battery?

The problem may be a failing motherboard, a power supply that is not delivering stable power, or a BIOS setting that is not saving correctly. Try resetting the BIOS to factory defaults through the BIOS menu itself, then replace the battery. If the issue persists, the motherboard may need repair or replacement.