How to replace the CMOS battery

If your computer is losing its time or date settings, or you are receiving a message CMOS Read Error, CMOS checksum error, or CMOS Battery Failure, first try leaving the computer on for 24-hours. In some cases, this can charge the battery and resolve your problem. This fixes most CMOS battery issues on computers left without power for several months. If this does not resolve your problem follow the steps below.

Locate your CMOS battery

Caution: When inside your computer make sure you are aware of ESD and its potential dangers.

CMOS batteryOpen the computer case and find the battery on the computer motherboard, verify that it is accessible and can be removed. Today, most computers use a coin cell CMOS battery as shown in the picture.

Tip: Some CMOS batteries may be held down by a metal clip or bar. This clip just holds the battery in place and the battery can still be removed by sliding it under the clip. Do not bend this clip to get the battery out.

If you are unable to locate your CMOS battery refer to your motherboard or computer documentation or contact your computer manufacturer for additional assistance in locating it.

Note: With some computers you may need to disconnect cables, remove drives, or remove other parts of the computer to get full access to the CMOS battery. See

Obtain battery information

Unfortunately, most manufacturers do not list the exact type and model of your CMOS battery; therefore, once you have located the battery, write down all information about the battery (Voltage, chemistry, wiring, and packaging). If possible, remove the battery and take it to the retail location.

Tip: The part number for this battery for most computers is CR2032.

Removing the battery

Caution: When inside your computer make sure you are aware of ESD and all its potential dangers.

If your computer is using a coin cell battery removing the battery is relatively simple. Use your fingers to grab on the edge of the battery and pull it up and out of the container holding it. Some motherboards have a clip holding the battery down. If your computer has this clip you may need to use one hand to move the clip up and the other hand to pull the battery out.

Unfortunately, not all CMOS batteries are removable; some manufacturers only allow a replacement battery to be added. If your computer does not have a coin cell battery and you are not sure how to remove the battery refer to your motherboard or computer documentation or contact your computer manufacturer for additional assistance in removing the battery or how to insert a new replacement battery.

Users with computers that do not have removable batteries only options to install a new battery will most likely also need to set a jumper when adding the new battery into their computer.

Insert the new battery

After purchasing a new battery, remove the old battery and replace it with a new battery.

Enter CMOS values

Once the battery is replaced turn on the computer and resetting the CMOS values to the defaults. After the values have all been entered make sure to save the settings before exiting. Many CMOS setups allow you to press a key (such as F10) to save values and exit all in one action.

Bad hardware

If after following all the above steps you continue to experience the same error when your computer starts or your computer is still unable to keep the stored values you are experiencing a more serious issues. Most likely causes are bad power supply or bad motherboard.

Additional information

  • See our CMOS definition for further information and related links on this term.