How to Check the Battery Level of the BIOS

by Jeva Anand

If you have owned your computer for a few years, you may notice certain problems, such as it may no longer remember the current time and date, certain peripherals may no longer load properly, and it may even refuse to boot at all, displaying error messages such as "No operating system" or "BIOS CMOS battery low cmos wrong." These symptoms suggest that the BIOS battery, a coin-shaped 3-V battery located on the computer's motherboard, is running low.

1. Reboot your computer and press "F10" or "Delete" when prompted to load the BIOS. Write down any custom hardware settings. Power the computer off and unplug any cables attached to it.

2. Use a Phillips screwdriver to remove the screws attaching the housing to the computer's chassis. Place the screws inside one of the housing's side panels or a small dish so you can find them easily. Touch your hand to an unpainted section of the chassis to discharge any static electricity.

3. Locate the BIOS battery and put it on a nonconducting surface. Power on the multimeter and set the rotary dial to "volts." If the multimeter does not automatically detect AC and DC current, specify "direct current."

4. Place the multimeter's contacts on the battery's poles -- the red one against its side and the black one on the top. If the battery's voltage output is less than 2 V, purchase a new BIOS battery.

5. Attach the old BIOS battery or its replacement to the motherboard. Screw the housing to the computer's chassis and reattach all cables to the computer.

6. Power on the computer. Press "F10" or "Delete" when prompted to load the BIOS. Load the default settings, if given the option. Load any custom hardware settings, referring to your computer's owners manual. Save any changes before exiting the BIOS screen.

Things Needed

  • Multimeter
  • Replacement BIOS battery
  • Phillips-head screwdriver


  • The BIOS battery is also known as the CMOS battery.
  • Keep your work area uncluttered so you do not misplace small parts such as screws.
  • The battery's location varies depending on the motherboard's type and manufacturer.
  • Depending on the type of motherboard, the battery attaches with a metal clamp, a plastic casing or a pluggable wire.
  • Refer to your multimeter instruction manual on how to set the device to measure direct current voltage, or VDC.


  • All custom hardware settings are lost when you remove the BIOS battery.
  • Electrostatic discharge can damage your computer beyond repair.
  • Don't over-tighten the screws.

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