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why does motherboard have batteryWhether you’re using a desktop computer or a laptop, your computer’s motherboard contains an integrated battery. Unlike a standard laptop battery, the motherboard’s battery doesn’t power your computer while you’re using it. Quite the opposite, actually – the battery is tiny and only active when you’re not actually using your computer.

The motherboard’s battery is used for low-level system functions like powering the real-time clock and storing a computer’s BIOS settings. On newer computers, the battery may only be used for the clock.

What’s a BIOS?

Every computer has a Basic Input/Output System, known as a BIOS. (Newer computers actually have UEFI firmware. UEFI replaces the traditional BIOS, but largely serves the same role as the BIOS.) The BIOS is stored in a chip on your computer’s motherboard. When your computer boots up, the BIOS starts up, performs a power-on self-test (POST), and initializes the computer’s hardware. The BIOS then passes control over to a boot loader located on a device – usually your hard drive, but a boot loader can also boot off a USB device or optical disc. The boot loader then loads your operating system – Windows, Linux, Mac OS X, or whatever else is installed on your computer.

The BIOS is responsible for low-level system tasks. You can enter your computer’s BIOS settings screen by pressing a key during boot. (On new computers that ship with Windows 8, UEFI is used instead, so you’ll need to access the BIOS from within Windows 8 How to Access the BIOS on a Windows 8 Computer How to Access the BIOS on a Windows 8 Computer Among the many changes coming with Windows 8 and new computers designed for it is a change in the way we access our computers’ BIOS. No longer do we press a certain key during the... Read More .)

The BIOS settings screen allows you to configure low-level settings for your computer’s hardware. For example, you may be able to overclock your computer’s CPU What Is Overclocking, And How It Can Help Your PC, Tablet, & Phone [MakeUseOf Explains] What Is Overclocking, And How It Can Help Your PC, Tablet, & Phone [MakeUseOf Explains] Provided that you have hardware from a manufacturer who understands those principles, you can do plenty to juice up your system, whether it be a computer, tablet, or smartphone. One of the best things you... Read More by adjusting settings like the CPU’s multiplier or front side bus (FSB). However, some motherboards may not allow you to control these settings at all. Other settings, like the computer’s boot order How To Change The Boot Order On Your PC (So You Can Boot From USB) How To Change The Boot Order On Your PC (So You Can Boot From USB) What happens when you start up your PC? In most cases (and putting it very simply), after the power switch has controlled the flow of electricity to the motherboard and the fans have started up,... Read More – the order in which the computer attempts to load operating systems from connecting hardware devices – and the system time can also be configured here.

why does motherboard have battery

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What’s a CMOS?

CMOS stands for complementary metal-oxide-semiconductor. Traditionally, BIOS settings were stored in CMOS RAM, which was powered by a battery when the computer was powered off. The battery was necessary because the settings would be lost if all power was lost, just as the data in your computer’s RAM is lost when it loses power.

why does motherboard need battery

Modern computers often don’t use CMOS RAM anymore. They store the BIOS settings in non-volatile memory, which means that the settings don’t need constant power to be saved.

Why Your Motherboard Needs a Battery

So if many computers now store BIOS settings in non-volatile memory that doesn’t need a battery, why do motherboards still come with batteries? Simple: Motherboards still include a Real Time Clock (RTC). This clock runs all the time, whether the computer is powered on or not. The real time clock is essentially a quartz watch, like the ones that people wear on their wrists (or used to wear on their wrists How Long Has It Been Since You Wore A Watch? [MakeUseOf Poll] How Long Has It Been Since You Wore A Watch? [MakeUseOf Poll] Geeks, teens and twenty-somethings mostly ditched their watches as soon as they got their first mobile phone. But these days even watch-lovers and old folk are finally leaving their watches at home. When did you... Read More  before cell phones came along.)

why does motherboard need battery

When the computer is off, the battery provides power for the real time clock to run. This is how your computer always knows the correct time when you power it on.

When the Battery Fails

As we all know from experience, batteries don’t last forever. Eventually, a CMOS battery will stop working. This may happen anywhere between two and ten years from when the computer (or its motherboard) was manufactured. If your computer is powered-on all the time, its battery will last much longer. If the computer is powered-off most of the time, its battery will die sooner – it’s using the battery more, after all.

If the battery fails on an older computer that stores its BIOS settings in CMOS, you’ll see error messages like “CMOS Battery Failure”, “CMOS Read Error”, or “CMOS Checksum Error” when you start the computer. You may also see more cryptic error messages, like “New CPU Installed” – the motherboard can’t remember that the CPU was installed previously, so it thinks it’s new every time you boot your computer.

why does motherboard need battery

On a newer computer that stores its BIOS settings in non-volatile memory, the computer may boot normally, but the computer may stop keeping track of time 3 Reasons Why Your Windows Computer Clock Loses Its Time 3 Reasons Why Your Windows Computer Clock Loses Its Time Read More when it’s powered off.

Replacing the Battery

In these cases, you’ll need to replace the CMOS battery. On most computers, it’s a small, silver disc located on the motherboard. The exact type of battery is usually a CR2032 battery – also used in calculators, watches, and other small electronic devices.

The battery is often removable, so it can be pried out and a new battery can be inserted. (Note that you should power off the computer and be careful of static electricity Your Sneakers Can Kill Your Computer: How Static Electricity Works [MakeUseOf Explains] Your Sneakers Can Kill Your Computer: How Static Electricity Works [MakeUseOf Explains] Static electricity is the number one computer hardware killer, and its everywhere! Panic aside, if you do any work with computer components - even as simple as upgrading your memory - you need to know... Read More when doing this sort of thing. Follow all the normal precautions for tinkering around inside of your computer.) However, on some computers, the battery may be soldered on, requiring a complete replacement of the motherboard or a repair performed by the manufacturer.

why does motherboard have battery

“Pulling the CMOS battery” – in other words, removing it and re-inserting it – may also be used as a troubleshooting step on computers that store their BIOS settings in CMOS RAM. For example, if a computer has a BIOS password 4 Creative Ways To Securely Password Protect Your Computer [Windows] 4 Creative Ways To Securely Password Protect Your Computer [Windows] Passwords are a first line defense to your privacy and often they are the only one. If you are concerned about your data, you will want this barrier to be high and strong. As has... Read More , removing the CMOS battery and reinserting it will cause the computer to forget the BIOS password and all its other settings. (If the computer stores its password in non-volatile memory, this won’t help – although there’s probably a way to reset it using a jumper on the motherboard.)

You can also reset the BIOS settings from within the BIOS settings screen, assuming the computer is booting properly and you’re not locked out of the BIOS setup screen with a password. This option may be named “Clear CMOS” or “Reset to Defaults.”

Do you have any other questions? Leave a comment or ask your fellow readers on MakeUseOf Answers!

Image Credit: Battery on Computer Motherboard via Shutterstock, BIOS Setup Utility via Richard Masoner on Flickr, Save to CMOS and Exit via Nick Gray on Flickr, Insides of Quartz Watch via Shutterstock, CMOS Checksum Error via Gordon Joly on Flickr, Expert Putting CMOS Battery in Motherboard via Shutterstock

  1. Dylan LaRose
    October 29, 2016 at 2:16 am

    can you hook up a light that also uses 3vs to the battery also?

  2. Roja
    October 20, 2016 at 5:41 pm

    It's very useful to me. Thanks a lot. Now I have a clear idea about bios.

  3. sunil
    February 5, 2016 at 3:21 am

    batter of my pc is dead the time doesn't work.my computer shuts down itself frequently. is it because this battery case?

  4. Sam
    January 17, 2015 at 11:11 am

    Thank you!

  5. Roystan Ang
    March 6, 2013 at 7:10 pm

    My Asus Rampage II Extreme is not remembering the BIOS settings I have saved. It resets everytime even though I have replaced with new batteries and still no luck. Any possible fix? Thanks in advance =)

  6. Ron Lister
    February 22, 2013 at 4:55 am

    I've had to change those before and had to move the jumper to the other pin to reset the CMOS too.

  7. Keith Swartz
    February 22, 2013 at 1:01 am

    Great read! Thanks for the write!

  8. Bob
    February 21, 2013 at 6:25 pm

    Had a case recently where a computer wouldn't boot. Went to manufacturer screen with options and then zip! Suspected power or hard drive - hard drive fine, pulled CMOS battery and replaced problem solved. Lots of the tech sites were talking about dead motherboard and other heavy stuff! (PC is HP DC7600) HAve had a few minor faults with this all of which people have said would be fatal. Usually fixed fairly cheaply :)

  9. Piseth Mao
    February 21, 2013 at 7:46 am

    Then from now on I should not leave my Windows Laptop off for so long!

  10. Kirby
    February 21, 2013 at 7:32 am

    I've used the troubleshooting technique you mentioned earlier. - “Pulling the CMOS battery” – in other words, removing it and re-inserting it – may also be used as a troubleshooting step..."

    It actually worked in resetting the BIOS settings.

    My motherboard battery took 8 years to run out off juice. However, until now, I still don't bother changing it. It won't cause significant problems to your OS anyways. It is quite annoying to constantly see the error messages each time I cold boot though.

  11. raj
    February 21, 2013 at 6:00 am

    my laptop does not show correct time......everytime i have to reset using internet time sync after turning on laptop.............is it related to cmos battery ??????????
    help me

    • Kirby
      February 21, 2013 at 7:34 am

      If your laptop has a motherboard battery, that's likely the cause. Have you spent a large amount of time NOT using your laptop?

      • raj
        February 23, 2013 at 8:48 pm

        i've been using my laptop regularly....and i am not sure about whether my laptop has any motherboard battery its HP G 62 ,I had purchased it two years ago

        • Chris Hoffman
          February 28, 2013 at 6:15 pm

          Yes, it's quite likely a battery problem.

    • Juan Pedro Secondo
      February 21, 2013 at 5:28 pm

      Some laptops were designed to be used on 110 volts 50 Hz. If you're using 220 volts 60 Hz that might change the clocking too.

      Your computer has a difference in time every time you start up or is it reset like 01/01/2000 for example. When the time is completely reset then the culprit is the battery.

      • raj
        February 23, 2013 at 8:54 pm

        i assume there is no such frequency problem

        Date shown by my laptop is close to actual date but time shown is always wrong.......so i guess its not battery problem

        • Juan Pedro Secondo
          February 25, 2013 at 4:10 pm

          The other culprit could be overclocking the CPU. That's forcing the CPU to work at a faster frequency than it was designed.

        • raj
          February 25, 2013 at 6:46 pm

          thanx for your reply...............would you please tell me about how to check whether its overclocked or not

  12. Paul G. Williams
    February 21, 2013 at 4:40 am

    This is really good to know, thanks.

  13. prasanth vikkath
    February 21, 2013 at 4:03 am

    Ya I know lol

  14. Ivan
    February 20, 2013 at 11:45 pm

    I think it should be ROM, not RAM.. ROM (Read Onlu Memory) and RAM (Random Access Memory) are "quite" different. We could only write data in ROM one time only, But in RAM we could store, wirte and read data manytime.. You should correct it.. But thanks for the info anyway.. :)

    • Craig Friday
      February 21, 2013 at 4:24 am

      but if it was ROM it could not be changed
      you can change your settings so it is RAM

      • Ivan
        February 21, 2013 at 8:42 am

        You should check this: http://en.wikipedia.org/wiki/BIOS :)

        • Chris Hoffman
          February 28, 2013 at 6:14 pm

          Well, the BIOS itself is stored in ROM, and the settings are stored in RAM.

  15. Doc
    February 20, 2013 at 10:27 pm

    "CMOS stands for complimentary metal-oxide-semiconductor." Actually, it's "complementary." "Complimentary" means giving out a compliment, praise, or approval; "complementary" means it complements, or completes, something. The two words have different meanings, but are often confused for one another.

    • Alberto Lerma
      February 21, 2013 at 5:34 am

      Usually when someone say something like this I show up this picture: http://www.flickr.com/photos/8311021@N03/3856828826/

      But in this case you're totally right, if you're trying to explain (and publish) something YOU SHOULD (at least) write it correctly.

    • Chris Hoffman
      February 28, 2013 at 6:13 pm

      Sorry, you're right. It's easy to miss such little typos while writing such a long piece, however. It's fixed!

  16. Anonymous
    February 20, 2013 at 10:17 pm

    WOW. I saw the battery in there when I was cleaning my pc. I thought about it for a minute, and wondered what it was for. It's funny that I see this post now and enlightened me. I love makeuseof.com.

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