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 issue. This often resolves CMOS battery related issues when a computer has been left off for several months. If this does not resolve your issue follow the steps below.

Locate your CMOS battery

Caution: When inside your computer make sure you're aware of ESD and all it's potential dangers.

CMOS batteryOpen the computer case and find the battery on the computer motherboard, verify that it will be accessible and that it can be removed. Most computers today use a coin cell CMOS battery, as shown in the image to the right.

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.

Obtain battery information

Unfortunately, most manufacturers will 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 location you plan on purchasing a new battery from. The part number for this battery for most computers is CR2032.

Removing the battery

Caution: When inside your computer make sure you're aware of ESD and all it's potential dangers.

If you're computer is using a coin cell battery similar to the above example picture. 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 had to move the clip up and the other hand to pull the battery out.

Unfortunately, not all CMOS batteries are removable; some manufactures only allow a replacement battery to be added. If you're not using a coin cell battery and are not able to determine how to remove it 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

Once you have purchased a new battery, remove the old battery (as instructed above) and replace it with the 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 it's likely that you're 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.