Your computer keeps forgetting the date and time, BIOS settings return to defaults after shutdown, or startup shows a CMOS checksum warning. Those are classic signs that the small battery on the motherboard is no longer holding settings while the system is unplugged.
Does This Affect You?
The CMOS battery powers the motherboard clock and helps preserve BIOS or UEFI settings when the PC has no external power. On most desktops it is a standard CR2032 coin cell, and it often lasts three to ten years. Laptops vary more: some use a coin cell in a holder, while others use a small wrapped battery with a cable connector or a hard-to-reach built-in design.
You will be working inside the device. Shut it down fully, unplug power, ground yourself by touching bare metal, and use a plastic spudger or fingernail rather than a metal screwdriver near the battery. Note the battery orientation before removing it. These steps are at your own risk; use a repair shop if the laptop is difficult to open or under warranty.
Replace the CMOS Battery in a Desktop PC
On most desktop motherboards, the battery is visible once the side panel is off.
- Unplug the PC and open the side panel.
- Find the small round silver battery on the motherboard, usually near the PCIe slots, chipset area, or board edge.
- Gently move the retention clip aside with a plastic tool or fingernail so the old battery pops up or slides out.
- Check which side faced up. The plus side is usually visible on a CR2032 holder.
- Insert the new CR2032 in the same orientation and press gently until the clip holds it.
- Close the case, reconnect power, start the PC, then enter BIOS/UEFI to reset date, time, boot order, and any custom settings.
Replace the CMOS Battery in a Laptop
Laptop access depends heavily on the exact model, so check the manufacturer service manual first.
- Shut the laptop down, unplug the charger, and remove the main battery if it is user-removable.
- Remove the correct bottom panel or service cover according to the manual, keeping screws organized.
- Locate the CMOS battery. It may be a small coin cell in a holder or a wrapped battery connected by a tiny cable.
- Disconnect or remove it gently, noting cable routing and orientation.
- Install the exact replacement type specified for the laptop model. Do not assume every laptop uses a bare CR2032.
- Reassemble, power on, enter BIOS/UEFI, and restore date, time, and any custom settings.
The real confirmation comes after the computer sits without power for several hours or overnight. If the clock and BIOS settings remain correct, the replacement is holding. If settings reset again almost immediately, the motherboard may be draining the battery or another power issue may be involved.
A CMOS reset also clears boot order. If the PC suddenly says no bootable device after replacement, go back into BIOS and put the normal Windows drive first. If only the time resets but other settings stay, or symptoms appear only after power outages, investigate the power supply or motherboard as well.
Sources
- Intel – What Is a CMOS Battery and How to Replace It (2024)
- Dell Support – Replacing the CMOS Battery on a Desktop or Laptop (2025)
- ASUS Support – CMOS Battery Replacement Guide (2024)