CMOS Battery Replacement Guide

Published 2026-10-16 · LuxuriousComputers Repair

Your computer shows the wrong date and time every time you turn it on. Or you see a CMOS checksum error on startup. Or your BIOS settings keep reverting to defaults — you set the boot order, save and exit, but the next time you power on, the settings are gone. These symptoms all point to the same component: the CMOS battery on the motherboard is dead or dying.

What the CMOS battery does

The CMOS battery is a small coin-cell battery (almost always a CR2032 lithium cell) on the motherboard that keeps the BIOS/UEFI settings and the real-time clock (RTC) running when the computer is powered off and unplugged. The BIOS chip itself is non-volatile — it retains the firmware without power. But the BIOS settings (boot order, clock speed, fan curves, secure boot state, and dozens of other configurations) and the system clock are stored in a small amount of volatile CMOS RAM that needs constant power to retain its data.

When the computer is plugged in (even when shut down), the power supply provides a trickle of standby power that keeps the CMOS RAM alive. The battery is the backup for when the computer is unplugged. When the battery dies, unplugging the computer (or the standby power being interrupted for any reason) causes the CMOS RAM to lose its contents. The settings reset to factory defaults and the clock resets to a default date (often January 1, 2000, or the BIOS release date).

Signs the CMOS battery is dead

• Clock resets on every power cycle: The system time is wrong every time you turn on the computer, even though you correct it. Windows syncs the clock with an internet time server after booting, so the time may appear correct once Windows is running — but during POST (before Windows loads) the time is wrong, and any BIOS-dependent timestamps are incorrect
• CMOS checksum error: A message during POST that says "CMOS Checksum Error," "CMOS Battery Failure," "CMOS Settings Wrong," or a similar variation. The BIOS detects that the stored settings do not match their checksum, which means the data was corrupted (typically because it was lost when the battery could not maintain power)
• BIOS settings reset: Custom BIOS settings (boot order, XMP profile, fan curves, virtualization settings) revert to defaults after every power cycle. If you have to re-enable XMP every time you turn on the computer, the CMOS battery is not maintaining the settings
• Boot issues: Some systems fail to boot or show "Press F1 to continue" on every startup because the BIOS detects the settings mismatch and pauses. Others boot normally but with incorrect settings (wrong boot device, wrong clock speed, disabled features)
• System age: CMOS batteries last 5 to 10 years in most systems. A computer that is 7 or more years old with any of the above symptoms almost certainly needs a new CMOS battery. Computers that are frequently left unplugged drain the CMOS battery faster

What you need

• A new CR2032 battery: This is the standard CMOS battery for virtually all desktop and most laptop motherboards manufactured in the last 25 years. CR2032 batteries are available at any electronics store, pharmacy, or supermarket. They cost one to three dollars. Buy a name-brand battery (Energizer, Duracell, Panasonic) — cheap off-brand CR2032 cells can have lower voltage or shorter life
• A small flat-head screwdriver or plastic spudger: To release the battery clip. A fingernail works on some motherboards if the clip is accessible
• Anti-static precaution: Touch the metal computer case before handling the motherboard to discharge static. Working on a non-carpeted surface reduces static risk

Desktop replacement steps

1. Shut down and unplug: Turn off the computer, unplug the power cord, and press the power button once (this discharges residual power from the capacitors). Leave it unplugged during the procedure
2. Open the case: Remove the side panel. On most tower cases, this is two thumbscrews on the back panel followed by sliding the panel toward the rear. The motherboard is now visible on the opposite side from the panel you removed
3. Locate the battery: The CMOS battery is a shiny silver coin cell, about the size of a nickel, sitting in a clip holder on the motherboard. On most ATX and Micro-ATX boards, it is located near the bottom-right area of the board, between the PCIe slots and the chipset heatsink. On some boards, it is near the RAM slots. It is usually the only coin cell on the board and is clearly visible. If a GPU or other card is blocking access, you may need to temporarily remove the card
4. Note the orientation: The battery sits with the positive (+) side facing up. You will see the CR2032 label and the + symbol on the visible face
5. Remove the old battery: The battery is held in place by a small metal clip that presses against the edge of the battery. Use a fingernail, small flat-head screwdriver, or plastic spudger to gently push the clip away from the battery. The battery will pop up slightly. Lift it out. Do not use excessive force on the clip — the clip is attached to the motherboard, and bending it too far can break the solder joint
6. Insert the new battery: Slide the new CR2032 into the holder with the positive (+) side facing up (same orientation as the old one). Push it down until the clip clicks over the edge and holds it in place. The battery should sit flat and secure in the holder
7. Close and power on: Reattach the side panel, plug in the power cord, and turn on the computer. The BIOS will likely show a CMOS checksum error or settings reset message on the first boot after the battery change — this is normal because the CMOS was cleared. Enter BIOS setup (usually by pressing Delete or F2 during POST), reconfigure your settings (boot order, XMP profile, date and time, and any other custom settings), save and exit. The settings should now persist across power cycles

Laptop CMOS batteries

Laptop CMOS batteries are the same CR2032 cell (or sometimes a smaller CR2016 or a wired battery pack), but accessing them requires partial or full disassembly of the laptop:

• On some laptops, the CMOS battery is under a small access panel on the bottom of the laptop (common on business-class laptops like Lenovo ThinkPads and Dell Latitudes). Remove a few screws, pop off the panel, and the battery is accessible
• On other laptops, the CMOS battery is buried deeper — under the keyboard, behind the motherboard, or attached to the underside of the board. These require removing the bottom cover and potentially disconnecting other components to reach the battery
• Some laptops (especially ultrabooks and MacBooks) use a wired CMOS battery that plugs into a header on the motherboard rather than a clip-mounted coin cell. The replacement battery must have the same connector type
• Check a teardown guide or service manual for your specific laptop model before attempting the replacement. iFixit and the manufacturer's hardware maintenance manual (if published) show the exact location and procedure for each model

After replacement

After replacing the battery and reconfiguring the BIOS settings, verify that the fix worked:

• Set the correct date and time in BIOS, save and exit, boot into Windows, then fully shut down the computer
• Unplug the power cord and leave it unplugged for 5 to 10 minutes
• Plug it back in and power on. Enter BIOS setup and check that the time is still correct and your custom settings are retained. If the settings held, the new battery is working correctly
• If the settings still reset after a new battery, the problem may be the battery holder (damaged clips that are not making good contact with the battery), a motherboard issue (damaged CMOS circuitry), or a BIOS corruption issue. Try reseating the battery to ensure solid contact with both the clip and the base contact

CMOS battery replacement in Columbus

Luxurious Computers replaces CMOS batteries on desktops and laptops — sourcing the correct battery, handling the disassembly (especially on laptops where access is not straightforward), and reconfiguring BIOS settings after the swap.