What a CMOS battery does and why you might need to replace it
Your computer has a small coin-shaped battery on the motherboard called a CMOS battery. It keeps your system clock running and stores basic hardware settings even when your computer is completely powered off. When this battery dies, your computer will forget the time, date, and sometimes boot settings — you'll notice the clock resets to 2000 or 2005 every time you restart.
Replacing it is a straightforward task that takes about 10 minutes and requires no special tools beyond a Phillips screwdriver. You do not need technical experience; you just need to follow the steps in order and take basic precautions against static electricity.
Key Takeaways
- A dead CMOS battery causes your computer to forget the time and date, or lose boot settings, but does not prevent the computer from starting.
- You need a replacement CR2032 battery (the most common size, costs a few dollars) and a Phillips screwdriver to open your case.
- The battery sits on the motherboard in a small circular holder and pops out by hand — you do not need to desolder anything.
- Before you open the case, shut down completely, unplug the power cable, and touch a metal part of the case to discharge static electricity that could damage components.
- After you insert the new battery, your computer will boot normally and you can reset the time and date in your system settings.
Gather what you need before opening the case
You will need a replacement CMOS battery. The vast majority of desktop computers use a CR2032 battery — a flat, round cell about the size of a dime. You can find these at any pharmacy, grocery store, electronics retailer, or online for $3 to $8. Buy one before you start; do not assume you have one lying around that still holds a charge.
You will also need a Phillips screwdriver to remove the side panel of your case. Some modern cases use thumbscrews instead, which you can turn by hand. Check your case before you start so you know which tool to grab.
Have a small, clean, flat surface ready — your desk or a table works fine. You will set small screws there while you work, so a surface where they will not roll away is helpful. Some people use a small bowl or a piece of paper with a grid drawn on it to keep track of where each screw came from.
Power down and protect against static electricity
Shut down your computer completely through the operating system. Do not just put it to sleep or restart — use the full shutdown option. Wait 30 seconds after the screen goes dark, then unplug the power cable from the back of the case. This ensures no power is flowing to the motherboard while you work.
Before you touch anything inside the case, touch a bare metal part of the case itself with your bare hand — the frame, a screw, or an unpainted metal edge. This discharges static electricity from your body. You do not need to do anything elaborate; just make contact for a second. If you are working in a very dry environment or on carpet, you can wear an anti-static wrist strap, but most people simply touch the case and proceed without issue.
Do not work on carpet if you can avoid it. A table or desk is better. If you must work on carpet, touch the case frame frequently as you work.
Open the case and locate the CMOS battery
Remove the side panel of your case. On most desktop cases, this is the left panel when you face the front. You will see either two or four screws holding it in place — remove all of them and set them aside in a safe spot. Slide the panel toward the back of the case or lift it straight out, depending on the design.
Look at the motherboard — the large circuit board that fills most of the case. The CMOS battery is a small, shiny, round cell about the size of a dime. It sits in a circular holder with a metal clip on one side. The holder is usually near the center or lower-left area of the motherboard, but the exact location varies by model. If you cannot find it, look for a holder labeled "CMOS" or "BIOS" on the motherboard itself, or consult your motherboard manual (you can find this online by searching your motherboard model number).
The battery is held in place by a small metal clip on one side of the holder. You do not need to remove the clip — the battery simply pops out when you press gently on the clip or lift the battery straight up.
Remove the old battery and install the new one
Press the metal clip on the side of the battery holder gently away from the battery. The battery will pop up slightly. Lift it straight out with your fingers. If the clip does not move easily, do not force it — just lift the battery straight up instead. It will come free.
Before you insert the new battery, check the orientation. The CR2032 has a flat side and a rounded side. Look at how the old battery was sitting — the flat side should face up (toward you) and the rounded side should face down (toward the motherboard). The new battery goes in the same way.
Insert the new battery into the holder, flat side up, and press gently until it clicks into place. The metal clip will hold it down automatically. You should hear or feel a small click. Do not force it — if it does not click after gentle pressure, remove it and check the orientation again.
Close the case and power on
Replace the side panel and screw it back in place. Make sure all screws are tight but do not overtighten them — snug is enough. Plug the power cable back into the case and into the wall outlet.
Power on your computer normally. It will boot just as it always does. You may see a message about the CMOS battery or BIOS settings being reset — this is normal and expected. Your computer will start up and function normally.
Once you are logged in, check the system clock. It may show the wrong time and date. Open your system settings and set the correct time and date. On Windows, right-click the clock in the bottom right corner and select "Adjust date and time." On Mac, open System Settings, click "General," then "Date & Time." Your computer will remember these settings from now on, even after you power off.
What to do if the new battery does not work
If your computer still forgets the time after you install the new battery, the problem may not be the battery itself. First, make sure the battery is fully seated in the holder — remove it and reinstall it to confirm it clicks into place. Check that you bought a CR2032 and not a different size by mistake.
If the battery is definitely installed correctly and you used a CR2032, the motherboard itself may have a problem, or the issue may be something else entirely (like a corrupted BIOS). In that case, contact the computer manufacturer or a local repair shop. Do not assume the battery is bad — many computers that seem to have a dead CMOS battery actually have a different issue.
If you are uncomfortable opening the case or if you have already tried these steps without success, taking your computer to a repair technician is a reasonable choice. The job takes them minutes and costs $20 to $50 in labor, plus the battery itself.
Frequently Asked Questions
Can I damage my computer by touching the motherboard?
You can damage components with static electricity, which is why you touch the case frame first to discharge yourself. Beyond that, the motherboard is fairly robust — you are unlikely to break anything by touching it carefully. Avoid dragging your fingers across the circuit board or touching the gold connectors on expansion cards. Just touch the battery holder and the battery itself, and you will be fine.
What if I cannot find the CMOS battery in my case?
Laptops and some small form-factor computers may have the battery soldered to the motherboard or located in a different spot. If you cannot find a removable coin-cell battery after looking for a few minutes, your computer likely requires professional service. Search your exact computer model plus "CMOS battery location" online, or contact the manufacturer.
Do I need to reset anything in the BIOS after replacing the battery?
No. The computer will boot normally and function as before. You may see a message about BIOS settings being reset to defaults, which is harmless. The only thing you need to do is set the correct time and date in your operating system settings.
How often do CMOS batteries need to be replaced?
A CMOS battery typically lasts five 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 power it off frequently, it drains faster. You will only need to replace it when it actually dies and your computer starts forgetting the time.
Is it safe to leave the case open while I work?
Yes, as long as the computer is powered off and unplugged. Never open the case while the computer is running or in sleep mode. Once you have unplugged it and waited 30 seconds, the case is safe to open for as long as you need.