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. Your motherboard features an integrated battery if you’re using an older desktop computer or laptop. However, the motherboard’s battery does not power your laptop while you’re using it, unlike a conventional laptop battery. It is mainly designed to power up the BIOS while you work.

Wait, does my computer have more than one battery? Well, the answer is again yes. While the main 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.

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. Normally, when the computer is turned down or loses power for some reason, this information is lost (dead battery, power failure, etc.). Even when the computer is turned off, the CMOS battery provides power to the CMOS chip.

This battery is typically a watch battery that can last for a year or more. During boot, you may receive error messages such as “CMOS checksum error” or “CMOS read error.” The CMOS battery in a computer is used to power the memory chip that includes the system configuration file and to keep and maintain the real-time RTC clock, which is the system clock. All initial settings for proper computer functioning are stored in the system configuration files.

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 capacities of 2.2TB or more, 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.

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 subsequently boots your operating system, whether it’s Windows, Linux, macOS, or something else entirely.

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.

Why do you need a battery for your motherboard?

Why do motherboards still come with batteries if many computers save BIOS settings in non-volatile memory? Simple: A Real-Time Clock is still included on motherboards (RTC).

Whether you turn the computer on or off, the battery is always on. A quartz watch, similar to an antique wristwatch, is what a real-time clock is. When the computer is turned off, the battery powers the real-time clock, and this 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; rather, it is intended to provide a small amount of power 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 very difficult without this specific functionality.

Without the CMOS battery, you would have to reset the clock every time you turn on the computer. The CMOS battery also provided the small amount of charge required to maintain the nonvolatile BIOS memory, which remembered BIOS settings between reboots on older systems. This information is typically stored in flash memory on modern systems and 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 normally last up to ten years. The CMOS battery lasts longer when you use your computer frequently. A battery in a computer that is mostly powered 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 boot normally on a modern machine that retains its BIOS settings in non-volatile memory, but 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?

Even if you’ve never handled computer components before, removing the CMOS battery is a rather simple task. Simply follow the steps outlined below. Remove any static discharge from your body before handling computer components. Simply touching the metal section of your computer case will suffice. Before proceeding, you should power off your computer, remove the power cable, and disconnect the battery if using a laptop. Take care to follow standard PC maintenance steps when opening your PC and be careful of static electricity. Note that 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. Typically, a few bolts must be unscrewed before the cover can be removed.
  • Make sure the motherboard is visible. Dust should 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 difficult. It is usually preferable to engage an expert.
  • To access the internal components, turn the laptop over, detach the bolts, and remove the case. Make sure 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 properly, tighten all case bolts and switch them on.


Non-Volatile RAM is another term for a CMOS battery (NVRAM). CMOS is a battery-powered semiconductor that is commonly found in computers. CMOS is commonly used in:

  • Digital logic circuits
  • Microprocessors
  • Static RAM (SRAM)
  • Microcontrollers

To answer our question, why CMOS battery is used in a 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 as well as all of its other settings.

  • The CMOS is a tiny memory that stores configuration information and BIOS settings for the system’s initialization.
  • Date and time, disc drive, and other configuration parameters are included. It is housed in a small compartment on the motherboard and is powered by a coin-shaped battery.
  • CMOS RAM is the traditional name for it.
  • Non-volatile BIOS memory is another name for it.
  • Because it is responsible for displaying the proper date and time, the CMOS battery is an RTC (Real Time Clock). The acronym CMOS refers to a complementary metal-oxide-semiconductor.

So now you know why your motherboard has a battery. The BIOS settings are retained by the CMOS battery on older computers. 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.

Arslan Ashraf
Arslan Ashraf is Computer Expert. He developed his passion for reviewing the latest tech products. He likes to review every single piece of Hardware. If you have any questions related to Tech Products. He'll be happy to answer you.

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