CMOS Battery Failure and Solutions

The CMOS battery, when fails, may result in some issues during booting up especially. Here is an article that will inform you about the signs and symptoms of CMOS battery failure and the time you need to replace it along with the process to follow while replacing it.


  • The CMOS battery may fail due to several reasons such as rise in temperature, voltage drop and even the working environment.
  • When the battery fails it will not be able to supply the necessary power to the CMOS which will change the settings of the BIOS firmware.
  • Significant issues during booting up of the computer may be noticed due to a failing or a failed CMOS battery.
  • The most significant sign of a failing CMOS battery is incorrect date and time of the system and the operating system failing to load during the boot up process.
  • The only solution to fix a failing or a failed CMOS battery is to swap it with a new one. It is however an easy and fast DIY project.

Effects of CMOS Battery Failure

When the CMOS battery fails, there can be some notable effects of it which will affect the overall performance of the system since the computer will not remember the settings or information needed for the boot up process.

One of the most significant effects of the battery failure is that the data and time of the computer system will be of long, long time ago. Another notable effect is that the operating system may be prevented from loading during the boot up process.

In addition to the above, there are also a few other unwanted instances that may be a result of a defunct CMOS battery as explained hereunder:

  • The setting of the NUMs lock, FDD and even the drive type may be changed
  • Messages like ‘Booting Error,’ ‘Unable to detect disk drive,’ ‘Cannot find printer’ ‘CMOS checksum error’ and others may be displayed
  • The computer may shut down abruptly
  • You may not be allowed to perform any tasks on your computer
  • The operational speed of the computer may be slow
  • The drivers may not function properly or may even disappear
  • You may not print out on the printer
  • The mouse might not respond properly
  • Connection to the internet may not be made
  • The system may emit a constant beeping sound
  • The keyboard may start acting strangely and the computer may not read the inputs and
  • The configuration of a customized keyboard may go back to the default one.
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The good news is that CMOS battery failure will not corrupt or delete any of your personal files because the storage system is not affected by such failure.

Reasons of CMOS Battery Failure

CMOS Battery Failure

The CMOS battery comes with a low voltage which is usually 3 volts. It is low because it does not need to supply power constantly but only when the system is switched off.

Typically, one of the most significant reasons for the CMOS battery to fail is the drop of the voltage below that level significantly. Another common reason for the battery to fail is its age.

Typically, a CMOS battery may last anywhere from 2 to 10 years depending on the power-off duration and the environment.

Any average battery will last for 3 to 5 years at least after which it will start showing signs of failure.

Sometimes increased temperature of the surrounding and the system in particular may also cause the battery to fail just as constant draining of current would.

Signs of CMOS Battery Failure

There are some good signs to look out for in order to identify whether or not the CMOS battery is failing or has failed already.

The most significant signs of CMOS battery failure are a reset date and time, computer not booting up and the BIOS firmware reverting to the default settings or has shut down.

In addition to that, all of the effects already mentioned earlier are signs of a battery failure.

Solutions of CMOS Battery Failure

When the CMOS or Complementary Metal Oxide Semiconductor battery fails or is dead, there is only one practical solution – to replace it with a new one.

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This is because you will not be able to reuse these batteries by recharging it like you may do with a lithium ion battery. If done, it may explode.

The process is pretty simple and you will simply need a screwdriver and a new CMOS battery.

However, before you start make sure that you disconnect the system from the electric mains and unplug all the cables from it including those of the peripherals.

Also find a good, flat and hard workspace to prevent building Electrostatic Discharge or ESD up and damage the components. Use a conductive foam pad as well to prevent ESD.

Protect yourself from static electric shock by rubbing your hands on a metal surface or wear an anti-static wrist band.

Now, there are specific ways to go about it and these steps may vary according to the system in question, especially while removing the cover of the casing. Otherwise, the steps are the same.

Ideally, the process to follow while replacing the CMOS battery from the motherboard of a computer includes:

  • Removing all cables but the power cord
  • Unplugging the power cord from the mains
  • Pressing the power button of the computer to drain any static current
  • Unscrewing and removing the side panel by holding it and pulling it gently outside
  • Locating the battery
  • Removing the battery by using the screwdriver needed
  • Replacing the new battery carefully in the right direction and in the same orientation as before
  • Replacing the side panel
  • Securing the screws of the side panel and
  • Reconnecting the power.

You must be very cautious while removing the battery from the motherboard. Since it is a very vital component, even the slightest carelessness may result in some serious damage to the motherboard.

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Finally, whether it is for your desktop computer or a laptop computer, you should check the system after replacing the CMOS battery.

Fix all cables and plug in everything carefully and turn the system on.

The Basic Input Output System or BIOS firmware should have gone back to the original settings and the date and time may still be incorrect.

Do not be alarmed even if you see a few drivers missing after the system boots up.

This is quite a natural thing to happen because when you remove the CMOS battery the computer system, or the BIOS in particular, forgets everything.

So, all you have to do now is reset everything once again to make your system normal as before.

If you still have some issues while booting up then it may be due to a faulty BIOS firmware in your system and certainly not due to the CMOS battery.


The CMOS battery provides the backup power to the BIOS firmware of the computer which may fail at times, as it is indicated in this article.

However, it is easy to replace it and restore the system to normalcy.

It is quite a simple, fast and easy DIY project to swap an old defunct CMOS battery with a new one.

About Puja Chatterjee

Puja ChatterjeePuja Chatterjee is a technical writer with extensive knowledge about computers. She graduated from BIMS. Her expertise includes technology writing and client relationship management gained through over 12 years of experience. Follow Her at Linkedin.

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