Reference number: CH000239

How to replace the CMOS battery

Issue:

How to replace the CMOS battery.

Cause:

Like any battery the computer CMOS battery can fail or lose its charge.

Solution:

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 attempt to leave 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 below steps.

Write down all system settings

Ensure that the information within your CMOS, if not already lost, is written down. If you're getting a CMOS error message or your time is not being saved your settings are already lost. Getting into the CMOS setup can be found on document CH000192.

Locate your CMOS battery

Open 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.  If you are unable to locate your CMOS battery you will need to refer to your motherboard or computer documentation and/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.

Additional buying information can be found on our battery buying tips page.

Removing the battery

Caution: While in the computer make sure you're aware of Electro Static Discharge (ESD), your computer is off, and that you're properly grounding yourself. Especially before removing the battery.

If you're computer is using a coin cell battery similar to the above example picture. Removing the battery is relatively simple. Simply 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 will 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 and/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 enter all values back into CMOS or set the values back to the default settings. Additional information about getting the values back to default can be found on document CH000970.

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.

If after following all the above steps you continue to experience the same error when your computer starts and/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.