Why Do Motherboards Have Batteries?

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

Well in the most simple of terms, the battery you find on a motherboard is called the CMOS battery. It serves a very special and critical purpose of keeping the BIOS settings as well as running the Real Time Clock (RTC) of your system.

Without this seemingly trivial battery, your motherboard and your PC in turn will simply not start.

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

In the following text I will talk in detail about the CMOS battery and why motherboards have them.

So Why Do Motherboards Have Batteries?

Let us start with the very basics first and try to understand a few key terms

What is CMOS?

CMOS stands for Complementary Metal-Oxide-Semiconductor. This is a very important chip where BIOS settings, as well as Real-Time Clock (RTC) is stored.

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

What is BIOS?

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

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

You can think of BIOS as a standalone operating system that basically 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 simply 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 suggest, 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. In fact, if your motherboard is malfunctioning or if your system does not start up properly chances are that you have a dead CMOS battery.

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

  1. It makes sure 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 at an average can last for about 5 years. So for 5 years, it can keep the settings in tact without any external power supply.

Removing the CMOS Battery Will Render Your Motherboard Useless

As explained, all the settings that 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 if you have performed a bad overclock then 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 on the latch on the battery socket. This should pop the battery out.

When taking the battery out, take note of the the negative “-” and the positive “+” terminals so that you know its orientation when plugging it back in.

Take note that removing the battery will also 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, then you motherboard will simply 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 easily fix a majority of the hardware related issues with the motherboard.

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

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

Symptoms of a Dead or a Failing Motherboard CMOS Battery

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

1. PC Turns on Sometimes, Sometimes it Does Not

The biggest symptom of a dying CMOS battery is that sometimes your PC will turn on normally and other times it will not turn on at all.

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 that the BIOS performs to check if all the hardware is in order.

If any critical hardware fails to initialize, the system will NOT pass the POST and will not load the operating system.

If the CMOS battery is dead, your motherboard will often flash 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 is showing the wrong time and date, this is a clear sign that your CMOS battery can be failing.

Recall from earlier that CMOS stores the System 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 reason why do motherboard have batteries is to essentially provide a trickle of power to the most essential CMOS chip 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 it is malfunctioning or removed.

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Author:

Atif Qazi
Atif Qazi is the founder of PCGuide101. He is a digital nomad who loves everything PC. He is a PC builder, tech enthusiast, engineer, and a lover of single player lore-rich RPG games.

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.

    Reply

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