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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

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