How to Test the CMOS Battery

Written by kallie johnson
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How to Test the CMOS Battery
Computers use CMOS batteries to maintain system information. (computer image by Orlando Florin Rosu from

The CMOS battery is an internal, rechargeable, computer battery for desktops and laptops that maintains computer system information such as the date and time. Just like any other type of battery, the CMOS can lose power and die over time. If you begin noticing an incorrect date or time on your computer, test the CMOS battery to determine if it needs to be replaced.

Skill level:


  1. 1

    Turn your computer on. Leave it on for 12 to 24 hours. When the computer is on, the CMOS battery is being recharged. Leaving the computer on for long periods of time helps ensure the battery is fully charged.

  2. 2

    Access the "System Setup" program on your computer. Enter the correct date and time. Click "OK" to exit system set-up.

  3. 3

    Turn the computer off. If your computer is a laptop, disconnect it from the power adaptor. Allow the computer to stay off for an hour.

  4. 4

    Turn on the computer. Insert the power adaptor into your laptop--if desired--and turn it on.

  5. 5

    Look at the date and time. If the are correct, the CMOS battery is working. If they are incorrect, the CMOS battery did not work and should be replaced.

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