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.
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.