Wanda Greaves

How to Detect CMOS Battery Failure of Your Computer

CMOS Battery FailureEvery computer has a small battery on its motherboard used to provide power to the CMOS on the computer. The CMOS (Complementary Metal Oxide Semiconductor) chip on your computer remembers everything like the disk drive, time and date, etc., so you don’t want to have a CMOS battery failure. The CMOS battery always provides power to the CMOS chip – i.e., even when your computer is OFF – to save all the settings. So, it is very important at the time of booting your computer and other tasks.

Learning to Detect a CMOS Battery Failure

The CMOS battery is a small battery fitted on the motherboard of your computer. It has a life of around five years. You need to use the computer regularly to extend the life of the CMOS battery. The computer power supply increases the availability of a standby current and hence increases the life of the battery.

If the computer is not plugged in regularly, the life of the battery is normally 3 years. However, the life of the battery gets extended to 5 years when you use it regularly. The battery provides power to CMOS memory and the real-time clock.

Signs of a CMOS Battery Failure

It is a 3V battery. If the voltage drops between certain levels, your computer loses the memory. The CMOS settings like date and time get changed. In some instances, the date and time get set to factory default. For example, your computer date will be set to factory settings, something like 12/01/2008.

  • All of the settings like drive type, FDD, NUMs lock, etc., in the computer setup will be changed. It may be causing booting problems since your computer does not remember information about the disk drive.
  • Your computer will show a message such as “Booting Error, unable to detect disk drive.”
  • The computer may be shutting down and will not allow you to perform any task.
  • Your computer may be too slow. It may be due to wrong time and date. It is time to replace the CMOS battery to correct these issues.
  • Some of the drivers may be missing or may not work properly. So, you may not be able to print out on the printer. Even if you install the printer driver correctly, your computer may keep on showing the message “can’t find printer.”
  • Your mouse may not respond properly. You may feel that your mouse might have gotten damaged and be ready to replace the mouse. But it might be solved by simply replacing the CMOS battery. Therefore, before ordering a mouse you can try the same mouse on another computer to check if it is actually defective. So, you can save your hard-earned money!
  • You may not be able to connect to the internet. It keeps on showing error when connecting to the internet. You need to check whether time and date are correct. If the date and time are wrong, try correcting. Then, check again; if the computer is still not connecting to the internet, you need to replace the CMOS battery.
  • If you hear a constant beeping sound when working with your computer, it is a sign that you need to replace the CMOS battery.

The computer will also display CMOS battery failure, CMOS read error, or CMOS checksum error, etc. If this happens, you need to switch on your computer and leave it on for a day. If the computer is not showing the errors after rebooting, the CMOS battery is charging. Otherwise, you need to replace the CMOS battery.

Where to Buy the CMOS Battery for Your Laptop or Desktop

You can make a visit to the local computer store to buy a CMOS battery for your computer or laptop or netbook. You can also buy the coin-shaped 3V CMOS battery from online stores. The premium CMOS battery is advised for trouble-free operation of the computer. It will last for more than 5 years. However, you can also buy a cheaper version of the 3V lithium battery for your computer. But, its life is much less when compared to the premium version. Therefore, it is suggested you buy a premium version of the battery for your computer.

Before buying a battery, you are advised to check the rating of your computer CMOS battery and order the same one from an online store. The online stores usually deliver the items within 5 to 7 days. If you can’t wait that long, you can also buy the premium version from the local computer store.

After Verifying CMOS Battery Failure, You Can DIY!

Replacing a CMOS battery in your laptop or computer is easy. If you are new to the computer or laptop, you can also seek the help of a local computer technician to replace the computer battery.

Items required for replacing the computer’s CMOS battery

  • Screwdriver set
  • Multimeter

Steps to replace the CMOS battery

First, switch off the computer or laptop and remove the power cord from the computer. It is also suggested to remove the battery pack from a netbook or laptop.

  • Remove the cover of the CPU or laptop using a star bit (Torx) screwdriver.
  • You can find a button type CMOS battery on the motherboard of your computer or laptop. Use the flat-head type screwdriver to slowly lift the button cell from the motherboard.
  • Use the multimeter to check the voltage of the battery (use a digital multimeter). If the voltage is less than 3V, your computer will not remember the CMOS settings, so it is time to replace the old battery with the new CMOS battery.
  • After replacing the battery in the same orientation, you can replace the computer cover and tighten the screws.
  • Plug in the power cord and switch the computer ON to check if it is working properly. However, after replacing the CMOS battery you need to enter the correct BIOS settings. So, after booting your computer, you need to enter the correct date and time.

Now your computer or laptop is ready for regular use! Again, it is suggested to use the computer regularly to extend its battery life.

Have you changed your CMOS battery in your computer? Let us know how it went!

Wanda Greaves

Wanda Greaves is the co-founder of, a website that helps people to find, use and do anything with their batteries, chargers or related electric devices.

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