Why Do Motherboards Have Batteries?

If you look closer at your motherboard, it has a peculiar little coin cell battery similar to what you see on a watch. This begs the question, why do motherboards have batteries?

Well, in the simplest terms, the battery you find on a motherboard is called the CMOS battery. It serves the unique and critical purpose of keeping the BIOS settings and running your system’s Real Time Clock (RTC).

With this seemingly trivial battery, your motherboard and your PC will start.

Having a battery on a motherboard seems counterintuitive since all motherboards are connected to the power supply unit and the wall socket for power anyways; why have the redundancy?

I will discuss the CMOS battery and why motherboards have them in the following text.

So Why Do Motherboards Have Batteries?

Let us start with the basics and try to understand key terms.

What is CMOS?

CMOS stands for Complementary Metal-Oxide-Semiconductor. This is an essential chip where BIOS settings and Real-Time Clock (RTC) are RTC) is stored.

Without CMOS, your BIOS will not start. And with BIOS, your PC will start.

What is BIOS?

Gigabyte motherboards have two BIOS chips. M_BIOS is the MAIN BIOS, and B_BIOS is the BACKUP BIOS in case the MAIN BIOS gets corrupted.

BIOS stands for Basic Input/Output. This is firmware installed in a separate chip on a motherboard.

BIOS is a standalone operating system that starts up all the hardware and performs all the necessary system checks before the actual operating system (Windows) takes over.

Like CMOS, without BIOS, your system will not start.

Also Read: How to Identify BIOS Chip on Motherboard?

The CMOS Battery

This brings us to the CMOS battery or the motherboard battery in question.

Motherboard CMOS Battery Labelled
CMOS Battery Labelled

The CMOS battery can easily be spotted on the motherboard.

As the name suggests, this is the battery that powers the CMOS chip, which, as stated earlier, stores the BIOS settings and the RTC.

Why is the Motherboard CMOS Battery Important

how to reset motherboard
CMOS battery

The CMOS motherboard battery is essential to the overall functioning of your PC. If your motherboard malfunctions or your system does not start properly, you may have a dead CMOS battery.

There are two main reasons why the CMOS battery is essential:

  1. It ensures that the BIOS settings are intact, EVEN if the PC is off or unplugged from the power supply.
  2. It makes sure that the Real Time clock is intact, EVEN if the PC is off or unplugged from the power supply

The CMOS battery, on average, can last for about five years. So it can keep the settings intact for five years without any external power supply.

Removing the CMOS Battery Will Render Your Motherboard Useless

As explained, all the settings you perform in BIOS are stored in the CMOS chip, and without the battery, neither the CMOS chip nor the BIOS chip will work, rendering your motherboard useless.

You Can Reset the Motherboard By Re-plugging the CMOS Battery

If you have recently made hardware changes, if your PC is acting up or performed a bad overclock, you can reset your motherboard by removing the CMOS battery and re-plugging it into the slot after 5 seconds.

Why Do Motherboards Have Batteries
CMOS Battery latch

You can remove the CMOS battery by pressing the latch on the battery socket. This should pop the battery out.

When taking the battery out, note the negative “-” and the upbeat “+” terminals to know its orientation when plugging it back in.

So as you know, removing the battery will reset your system clock.

Read in Detail: How to Reset Motherboard?

A Dead Motherboard Battery Means a Dead Motherboard

It is as simple as that. If you have a dead CMOS battery, your motherboard will not work.

Often when the motherboard does not work or if it comes dead on arrival, the issue is as simple as a dead CMOS battery.

Therefore, replacing the CMOS battery with a new one can quickly fix most of the hardware-related issues with the motherboard.

The CMOS battery is a CR2032 lithium coin cell battery, standard across all motherboards.

Also Read: How to tell if the motherboard is terrible or dead?

Symptoms of a Dead or a Failing Motherboard CMOS Battery

There are many telltale signs of a failing CMOS or motherboard battery. Some of the hallmark signs are as follows:

1. PC Turns on Sometimes, but Sometimes it Does Not

The most prominent symptom of a dying CMOS battery is that sometimes your PC will turn on usually, and other times it will not.

You may hear the fans turn on, but the screen will be blank.

2. PC Will Not Go Past POST

motherboard flashing leds
Your motherboard may Flash LEDs if the CMOS battery is dead.

POST stands for Power On Self Test. Think of this as the startup tests the BIOS performs to check if all the hardware is in order.

If critical hardware fails to initialize, the system will NOT pass the POST nor load the operating system.

If the CMOS battery is dead, your motherboard will often flash an LED, or if you have a beep code speaker, it will beep the relevant code of motherboard failure.

3. Windows Showing Wrong Time and Date

If you occasionally find that your Windows operating system shows the wrong time and date, this is a clear sign that your CMOS battery can fail.

Please remember from earlier that CMOS stores the System’s REAL TIME data and time EVEN when the PC is turned off or removed from the power supply.

Hence, an incorrect date or time can indicate your CMOS battery is dying.

Also Read: Why Does My PC Randomly Turn Off?

Final Words

So the motherboard has batteries to give the essential CMOS chip a trickle of power for keeping the BIOS and the Real Time Clock settings intact.

So while the motherboard battery may seem trivial, it can render your entire motherboard into nothing but a brick if malfunctioning or removed.

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Ojash Yadav is the lead technical writer and resident tech guru at PCGuide101. He is a computer science graduate with over 8 years of experience in the IT field and a wealth of knowledge about computer peripherals. He has a passion for breaking down complex technical concepts and his goal is to make sure that our readers understand the technical details of the products they're interested in without getting lost in jargon. Ojash has over a decade of experience writing about the latest and greatest in the tech world, his articles have been featured in many popular tech publications and he's known for his thorough and unbiased reviews. He conducts extensive research and testing on the latest products to ensure our readers always get the most reliable information possible.

1 thought on “Why Do Motherboards Have Batteries?”

  1. Thanks for the informative article. I’ve been around computers since the mid 80’s but only as a user. Now having to learn more about them so I can build some work computers.


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