What Is a CMOS Battery?

A CMOS battery is not something that most of us will ever have to deal with. However, if you are among those unfortunate who are experiencing random computer crashes or power outages, this blog post is for you. Continue reading and learn about what is a CMOS battery and what its functions are.

What is a CMOS battery, and what are its functions?

Many have wondered what is CMOS battery. CMOS stands for “complementary metal-oxide-semiconductor”, a small, coin-shaped battery that provides power to the motherboard or BIOS “Basic Input/Output System in a computer during periods when the computer is turned off. It’s also known as an RTC battery, short for real-time clock.

CMOS batteries are used in both laptops and desktop PCs. However, they are more common in a laptop. This is because that laptops are generally unplugged for a longer duration than desktop PCs. The majority of desktop PCs are rarely switched off from the mains supply.

When your laptop is plugged in, the CMOS battery gets recharged. The battery only loses charge when your laptop is disconnected. The average life of a battery is 2 to 10 years after it has been manufactured. The longer your laptop is plugged in, the longer its battery will last.

How do you know if your CMOS battery is failing?

You might be experiencing symptoms of CMOS battery failure if your laptop has the following:

  • It’s difficult to boot up, or it might not boot up anymore.
  • If you detect a continuous beeping or buzzing noise from the interior of the computer.
  • The date and time changed back to their original default setting. The computer is not able to keep its current date and time.
  • The keyboard is acting weird or won’t respond sometimes. You are unable to move the mouse or click any icon.
  • A CMOS failure might also delete any drivers that you installed on your computer, such as those for your home printer.

If any of the signs or symptoms mentioned above are experienced, you should either find a replacement CMOS battery immediately or have your laptop sent to a professional for repair. It could be possible that it can no longer hold its charge and needs replacing.

How to replace the CMOS battery in a laptop?

You may follow the step-by-step procedure below if you wish to change the CMOS battery in your laptop or ask your authorized laptop technician for assistance as long as you are able to pay for its service fee.

Step 1: Shut down the laptop and make sure to disconnect or unplug all cables.

Step 2: Flip the laptop and remove its casing. You will need a screwdriver to loosen all the screws that hold the casing in place.

Step 3: Locate the laptop’s battery and remove it. Look out for something that is typically long, hefty, and oblong in form.

Step 4: Removing the laptop’s battery will expose the motherboard. When working around the motherboard, be extremely cautious. The motherboard is the most significant component of your computer, and if you harm it, you could severely damage the laptop. The next thing you will do is to locate the CMOS battery. Look for a tiny holding socket that contains a shiny and round feature that looks like a button or coin. Once located, remove the CMOS battery very carefully. Before removing the battery, take a note of its position, so you know which way to install the new one.

Step 5: Insert the new CMOS battery and make sure it’s in place.

Step 6: Return the laptop battery and then reattach the casing part and screws in their respective places. Be sure that all of the screws are properly tightened.

Step 7: Plug the laptop into a power source and turn it on. This may require you to set the new date and reinstall the drivers as the BIOS has set it back to the default setting.


The CMOS battery is an essential component in your computer that stores information about when your clock was last set. These batteries are crucial because if they’re drained, they could lead to a loss of data on the computer. It’s important to take care of these little button coin batteries so that you can keep all your precious memories safe in your device. It is always best to replace the battery as soon as it shows signs of failure. Be sure to use a battery that is compatible with your desktop or laptop. To make sure you’re always prepared for the worst, it is a good idea to have an extra CMOS battery on hand.

About the author, Phil Borges

Phil Borges is a battery aficionado. He's written extensively about batteries, and he loves nothing more than discussing the latest innovations in the industry. He has a deep understanding of how batteries work, and he's always on the lookout for new ways to improve their performance.