How to Tell if a CMOS Battery is Low

CMOS battery

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Is your computer's clock falling behind or continually incorrect even though you might have reset the time? Read these tips to learn how to tell if a CMOS battery is low.

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Instructions

Difficulty: Moderately Easy

Things You’ll Need:

Computer

Step1

The CMOS or "Complementary Oxide Metal Semiconductor" is the storage unit for the BIOS (Basic Input Output System) of your computer. This keeps you from losing your computer's motherboard information each time you shut down.

Step2

When the CMOS battery does get low, it will not be a crisis initially. You will have some time to open your computer and find out what replacement battery you will need.

Step3

With some computer models, you will receive an error message on your screen initially at startup. This message varies by manufacturer. You may also see a prompt at start up that states "Press F1 for setup or F2 to load default values." Know that this could vary by computer brand.

Step4

Sometimes the computer will not show signs of failure at each boot up. It may be more random at first. Or, your computer may get to a certain point in the start up process and then freeze. And, rebooting does not seem to help this problem.

Step5

Eventually, when the battery is drained entirely, it will not be able to save any of your settings and then the CMOS will need to be replaced.

Tips & Warnings

Do not ignore error messages.
Listen for more than one beep code when starting your computer. If there is more than one beep at start up, it can be your computer signaling you that there is a problem.
This is just a general overview of warning signs. Consult your motherboard manual for exact, specific information.
Always consult a computer professional if you are unsure or the problem remains after repair attempts.