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Why CMOS Battery is used in Motherboard?

Did you know your computer’s motherboard has a battery? It’s quite a jaw-dropping discovery, but...

Why CMOS Battery is used in Motherboard?

Did you know your computer’s motherboard has a battery? It’s quite a jaw-dropping discovery, but the answer is yes; the mother circuit has a battery embedded into it. If you use an older desktop computer or laptop, your motherboard features an integrated battery. However, the motherboard’s battery does not power your laptop or personal computer while using it, unlike a conventional laptop battery. It is mainly designed to power up the motherboard BIOS while you work or even when the system isn’t in the working state.

Wait, does my computer have more than one battery? Well, the answer is, again, yes. While the central computer battery powers all of the components from the CPU to the hard drive and tends to be one of your computer’s largest and heaviest parts, the CMOS battery powers merely the BIOS and is usually coin-sized and lives on the motherboard. The battery (known as “CMOS”) is tiny and only activates when your computer is turned off. So, why CMOS battery is used in the motherboard? Let’s have a look.

Key Takeaways

  • CMOS battery is a small coin-shaped battery that is attached to the motherboard and provides power to the CMOS chip, which stores the BIOS settings and the system clock.
  • CMOS battery is usually a 3V lithium battery, such as CR2032, CR2025, or CR2016, and it can last for several years before needing replacement.
  • CMOS battery can be replaced by locating it on the motherboard, removing it from its holder, and inserting a new one with the same specifications and polarity. The system should be powered off and unplugged before doing this.
  • CMOS battery replacement can help fix issues such as incorrect date and time, BIOS errors, boot failures, or system instability. It can also improve the system’s performance and security.
  • CMOS battery replacement can also reset the BIOS settings to their default values, which may cause some problems or changes in the system’s configuration. Users should backup their BIOS settings and data before replacing the CMOS battery.

Know these before heading further

What is CMOS?

The CMOS (complementary metal-oxide-semiconductor) chip on the motherboard stores the BIOS configuration, date, time, and other information that the computer requires during startup. In this way, it acts as a device that stores necessary instructions or initial functioning files for the motherboard so it can start and run accordingly. You may consider it similar to RAM since the RAM stores instructions for the CPU or processor. At the same time, CMOS does the same operation but for the motherboard. 

What is BIOS?

Older computers use a BIOS, or Basic Input/Output System, contained in a chip on the motherboard instead of UEFI. The BIOS starts up when your computer turns on, runs a power-on self-test (POST), and initializes the machine’s hardware. The BIOS then hands over control to a boot loader, which is normally located on your hard disc. Remember, you can also use a boot loader to boot from a USB drive or an optical disc. The boot loader boots your operating system, whether it’s Windows, Linux, macOS, or anything else.

The BIOS is in charge of low-level system operations. You can access your computer’s BIOS settings panel by pressing a key during Boot. The BIOS settings page lets you customize low-level hardware settings for your computer. Some choices are universal, while others vary by the motherboard manufacturer. Changing the computer’s boot order—the order in which it loads operating systems from attached storage—is an example.

What is UEFI?

The BIOS was replaced by the Unified Extensible Firmware Interface (UEFI) specification. UEFI is an industry-wide standard that was agreed upon by chipmakers like Intel and AMD, as well as Microsoft and PC manufacturers. Due to its origins in the IBM-compatible era of personal computers in the 1980s, BIOS has some limitations.

UEFI addresses these issues by introducing features like compatibility for discs with 2.2TB or more capacities, 32-bit and 64-bit modes, and Secure Boot. This last feature is a method of securing the PC. Secure Boot ensures that malware does not exploit a computer’s boot process. It does this by checking that any code executed at the Boot has a valid digital signature.

Why CMOS battery is used in motherboard?

Why do motherboards still have batteries if many computers save BIOS settings in non-volatile memory? Simple: A Real-Time Clock is still included on motherboards (RTC) due to a number of certain reasons. The battery is always on whether you turn the computer on or off. Like an antique wristwatch, a quartz watch is what a real-time clock is. When the computer is turned off, the battery powers the real-time clock, which is how your computer knows what time it is every time you turn it on.

The CMOS battery is not intended to provide power to the computer while it is running; it is intended to give a small amount of energy to the CMOS when the computer is turned off and unplugged. This serves the primary purpose of keeping the clock running even when the computer is turned off. It would have been complicated without this specific functionality. In short, you can consider the CMOS battery as a power source that keeps some part of your system running even when it is turned off in actuality. 

But what if we don’t have a CMOS battery? Well, without the CMOS battery, you would have to reset the clock every time you turn on the computer, and it’s the one result of the battery’s absence. The CMOS battery also provided the small amount of charge required to maintain the non-volatile BIOS memory, which remembered BIOS settings between reboots on older systems. This information is typically stored in flash memory on current-era modern systems. It does not require a charge to be maintained.

When should your motherboard battery be replaced?

Batteries, as we all know, do not last indefinitely. A CMOS battery will eventually fail; they usually last up to ten years. The CMOS battery lasts longer when you use your computer frequently. A battery in a computer that is powered chiefly off, on the other hand, will die sooner—after all, it is consuming the battery more. If the battery on an older computer fails and the BIOS settings are stored in CMOS, error warnings such as:

  • CMOS Battery Defect
  • Error in ACPI BIOS
  • Read Error in CMOS
  • Error CMOS Checksum
  • Installed a new CPU

This one is particularly perplexing at first, but the solution is straightforward. The motherboard cannot recall that the CPU was previously fitted without a battery powering the BIOS. As a result, every time you turn on your computer, it thinks it’s brand new. The computer may generally boot on a modern machine that retains its BIOS settings in non-volatile memory. Still, it may lose track of time when it is turned off. It can cause problems with connections and downloading updates, so it’s worth updating.

How do I get the CMOS battery out?

Removing the CMOS battery is a relatively simple task, even if you’ve never handled computer components. Simply follow the steps outlined below. 

Take these precautions

Before going into the actual procedure, you first have to take some precautionary steps to maintain safety. Those steps include the following:

  • Remove any static discharge from your body before handling computer components.
  • Power off your computer.
  • Remove the power cable.
  • Disconnect the battery if using a laptop. 
  • Follow standard PC maintenance steps when opening your PC, and be careful of static electricity. 

Note: The battery may be soldered onto the motherboard in some computers.

How to remove the CMOS battery on a desktop computer?

  • Remove the cover of the PC case to see what’s within. Because it varies depending on the situation, consult the instructions. A few bolts must be unscrewed before the cover can be removed.
  • Make sure the motherboard is visible. Dust must be removed.
  • On the motherboard, search for a battery. It should be coin-sized.
  • Remove the battery carefully from its enclosure. Keep track of the battery’s positive (+ve) and negative (-ve) sides. The bright side is usually on top.
  • Replace the cover on your computer cabinet.

How to remove the CMOS battery on a laptop?

  • Because of its small size and additional screws, removing the CMOS battery from a laptop is a little more complicated. It is usually preferable to engage an expert.
  • To access the internal components, turn the laptop over, detach the bolts, and remove the case. Ensure the computer is turned off and the charging wire is unplugged.
  • Remove the computer’s battery first, then look for the CMOS battery on the motherboard. It should resemble a desktop PC in appearance.
  • Remove the CMOS battery with caution.
  • Remove the new battery in the same manner as you did the old one.
  • Replace the laptop case and reinstall the laptop battery.
  • To make sure your laptop is working correctly, tighten all case bolts and switch them on.


CMOS is a battery-powered semiconductor that is commonly found in computers and several other devices to store motherboard-required information or instructions. It works even when the system is tuned off with the help of a CMOS battery. This is the exact reason why CMOS battery is used in motherboard. Essentially, the CMOS battery powers the real-time clock, whether the device is turned on or off. Additionally, removing and re-inserting this will delete the device’s BIOS password and all of its other settings.

So now you know why your motherboard has a battery. The CMOS battery on older computers retains the BIOS settings. The CMOS battery powers the PC’s clock on newer devices. Replacing the CR2032 battery on your motherboard is simple, albeit it may be fixed to the motherboard in some situations. Fortunately, CR2032 batteries are widely available; thus, replacing them should be simple. In addition, we have also talked about the method to replace the CMOS battery for both PCs and laptops. If the system’s battery is dead, you can easily follow the above-given process to replace it.

Frequently Asked Questions

What is the need for CMOS batteries in computers?

The CMOS battery powers the CMOS chip on the motherboard so the board’s BIOS can load anytime, even when the computer is off. In this way, the PC or laptop can boot up the necessary data and do certain operations. For example, the real-time clock is still working in the background that needs to be kept powering up to maintain accurate time.

What happens when a CMOS battery dies?

The answer to this question lies in the operation of the CMOS battery, which is used to keep running certain operations like motherboard booting up and running a real-time clock. You will probably need to reset the time and date if the battery dies. Moreover, the mother circuit may face some issues restarting again due to an unstable booting-up process.

Sajid Ali

CEO, Lead Writer

Sajid Ali is a tech enthusiast and gamer who loves to write reviews about gaming hardware. He has a passion for staying up-to-date with the latest technological advancements and loves sharing his knowledge with others. Sajid studied Intermediate Computer Science at Degree College and went on to earn his Bachelor's in Computer Science from GSC. In his free time, you can find him testing out new hardware and software, or playing the latest video games. Sajid's in-depth understanding of computers and his love for gaming make him the perfect author to turn to for all things tech and gaming.