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What is a CMOS Battery? How to Remove and Replace One in a Laptop

What is a CMOS Battery? How to Remove and Replace One in a Laptop

Zach Cabading
Reading time: 11 minutes
You don’t have to abandon ship when your laptop starts to malfunction. HP laptops enable you to make upgrades when a piece of hardware needs replacing. You don’t always need to shovel out cash for a brand new laptop. Just buy a replacement part and install it...with caution.
If you’ve owned your laptop for several years, it’s possible your computer is malfunctioning because the CMOS battery died. The CMOS battery is a piece of hardware that’s unique to laptops. When it dies, it could cause your laptop to encounter problems booting up.
Thankfully, it’s easy to install a new CMOS battery in your laptop. Here we’ll dive into three topics:
1. What does a CMOS battery do?
2. How do I diagnose a CMOS battery failure?
3. How do I replace the dead CMOS battery with a new one?
Wait, my laptop has more than one battery? In short, yes. While the main laptop battery powers all of the components from the CPU to the hard drive and tends to be one of the largest and heaviest parts of your laptop, a CMOS battery powers just the BIOS, and is usually coin-sized and lives on the motherboard.

Computer BIOS

To understand the importance of a CMOS battery, you first need to understand what your computer BIOS is.
Every computer has BIOS pre-programmed into its hardware. It’s different than an operating system. Operating systems can be installed, uninstalled, and updated long after you’ve bought the computer. BIOS is something that’s integrated into the computer while it’s being manufactured.
BIOS stands for “Basic Input/Output System.” What exactly does it do? Basically, it manages the essential functions of your computer.
All computers function through a process of inputs and outputs. Let’s say, for example, that you’re opening up a software program:
1. Your CPU sends an instruction to your hard disk to retrieve the software program from storage; that’s an input.
2. Your hard disk retrieves the software program data and sends it back to your CPU; that’s an output.
3. Your CPU runs the program. It sends instructions to your graphics processor telling it what image needs to be created; an input.
4. Then your graphics processor sends instructions to your monitor telling it how to arrange the pixels on the screen to create the image; an output.
Everything your computer does can be boiled down to an input or output. The BIOS is tasked with managing your computer’s exchange of inputs and outputs, mostly when you’re booting up your computer. BIOS instructs your computer on how to boot up the operating system, and it also operates the peripherals (like the mouse and keyboard) [1].
You press the power key to turn on your laptop, right? Well, how’s your laptop supposed to process the power key when the laptop is turned off? That’s what the BIOS is there for. It performs basic functions for your computer while your computer is still waking up. Pressing the power key is a basic input. Booting up your operating system is the basic output.
If you’re a PC gamer, you might be interested in learning how to overclock your computer to boost your processing speed while you’re gaming. You can program your computer for overclocking by adjusting the BIOS settings. We’ll teach you how to use BIOS to overclock at the end of this article.

Laptop CMOS chip

CMOS stands for “Complementary Metal Oxide Semiconductor.” The CMOS battery powers the BIOS firmware in your laptop [2].
BIOS needs to remain operational even when your computer isn’t plugged into a power source. That’s where the battery comes in. When your computer gets unplugged, BIOS relies on the CMOS battery for power.
You’ll find CMOS batteries in both laptops and desktop PCs, but it’s used more frequently in a laptop. That’s because laptops are usually unplugged for a longer amount of time than desktop PCs. Most desktop PCs are unplugged from their power source very infrequently.
The CMOS battery gets charged whenever your laptop is plugged in. It’s only when your laptop is unplugged that the battery loses charge. Most batteries will last 2 to 10 years from the date they’re manufactured. The more you leave your laptop plugged in, the longer your battery will last.

How do I know my CMOS battery failed?

Here are the CMOS battery failure symptoms:
  • The laptop has difficult booting up
  • There’s a constant beeping noise from the motherboard
  • The date and time have reset
  • Peripherals aren’t responsive or they don’t respond correctly
  • Hardware drivers have disappeared
  • You can’t connect to the internet
When your CMOS battery fails, your BIOS firmware will shut down and revert to its default settings [3].

Boot up problems and incessant beeping

As we mentioned previously, BIOS is largely responsible for booting up your computer. Without the battery, your laptop may have a very difficult time booting up or it may not boot up at all. You also might hear a constant beeping noise from the motherboard, another indication of a battery failure.

Time and date from long, long ago

If your laptop manages to boot, you might notice that the date and time have reset. Most likely, they’ve reset to a date long in the past. Even when your computer is shut off, BIOS maintains a real-time clock that tracks the date and time. CMOS (which is sometimes referred to as a real-time clock, in and of itself) is responsible for maintaining that procedure. So if the date and time have mysteriously reset, that’s a very good sign that the CMOS battery died.

Keyboard acting wonky

It’s possible that your peripherals don’t respond - you can’t move your cursor or click on any icons or the laptop won’t read any of your keyboard inputs.
Or, your peripherals could be thrown out of whack; your cursor is inaccurate and your key inputs prompt strange responses from the operating system.
Or, your customized keyboard configuration has reset to the default one. These are all signs of CMOS failure, since BIOS is responsible for managing peripherals at startup.

Drivers disappear

If you’ve installed any drivers on your computer, like those used for your home printer, a CMOS failure may cause those drivers to disappear (you’ll have to re-download and re-install them).

No internet connection

Battery failure may also prevent you from connecting to the internet. BIOS is tasked with maintaining hardware and network drivers.
One thing you should be relieved about is that CMOS failure typically won’t cause you to lose any of your personal files. Nothing in storage is affected. You’ll still have all of your pictures, videos, and documents waiting for you as soon as you’ve replaced the battery.

How to remove and replace the CMOS battery

Let’s remove that pesky ol’ CMOS battery and replace it with a new one. It’s a relatively simple process. You’ll only need a few supplies:
  • Screwdriver (Phillips or flathead, depending on the type of laptop you have)
  • Compressed air
  • New CMOS battery
  • ESD mat
You can purchase a new CMOS battery online for a very reasonable price, usually between $1 and $10. They are also available, along with ESD pads, at many local retailers like Target, Fry’s Electronics, Best Buy, and office supply stores.

1. Find a good workspace

Your laptop components can be damaged by electrostatic discharge (ESD). To avoid building up a charge, don’t work on a carpeted surface. Work on a flat, hard surface. In fact, it’s best to work on a conductive foam pad, if possible. These pads will prevent ESD.
It’s possible that there’s static electricity in your hands. Before you start working, rub your hands on a metal surface to get rid of the charge. Better yet, if you have an anti-static wrist band you probably want to put that on for this DIY project.

2. Disconnect everything

Shut down your computer and unplug it from its power source. Unplug any and all cables from the laptop, including peripherals.

3. Remove the laptop casing

Flip the laptop over. Use the screwdriver to remove the screws holding the laptop casing in place. Remove the casing once you’ve unscrewed it.
Note that on some laptops, there’s only one large casing that needs to be removed. On other laptops, there are several smaller casings that give you access to different computer components. If you’re not sure which casing gives you access you what, you might need to unscrew all the casings and do some exploring.
Pro tip: Have a couple of small bowls to hold the screws you remove. Remember, you’ll need to find them all when it’s time to put them back in so you don’t want them rolling off the table and getting lost.

4. Remove the battery

You don’t want the computer to accidentally turn on while you’re working on it. Usually, the battery is long, heavy, and shaped something like a brick.

5. Remove the CMOS battery

By this point, you should see the motherboard. Be very careful when you’re working around the motherboard. This is the most important hardware in your computer and you could seriously damage the laptop if you damage the motherboard.
The CMOS battery is shiny and round. It looks like a button or coin, and it’s usually placed within a small holding socket. Remove the CMOS battery - it slides out of the socket just like the batteries in your mouse.
Pro tip: Before you remove it, make sure to take note of the battery’s orientation so you know which way to put in the new one.

6. Insert the new battery

Place the new battery in the same location. Make sure you place the new battery in the exact same orientation as the old one.

7. Reattach the casings

Rescrew each of the casings within the computer. Reinstall the battery. Replace the exterior casing.

8. Test the laptop

Plug your laptop back into its power source and turn it on. BIOS should have defaulted back to its original settings, so don’t be alarmed if the date and time are still incorrect, or if there are drivers missing. You will need to reset the time and reinstall the drivers.
Pro tip: Your laptop shouldn’t have any problem booting up now. If it does, it might be your BIOS firmware that’s faulty and not your CMOS.

How to replace the CMOS battery in a desktop computer

Have a desktop computer with a CMOS issue? Read HP’s quick guide on how to replace the CMOS battery in a desktop computer. It’s even easier to replace the battery in a desktop because desktop computers usually have a more accessible motherboard.

Use BIOS to overclock your computer

All computers have a programmed “clock speed.” Clock speed refers to how fast a computer processor can read incoming electric pulses of information. The most powerful processors have fast clock speeds.
If you’re a PC gamer or a creative professional, you want an ultra-fast processor. PC games and creative applications, like the Adobe Creative Suite, require your CPU to process and render large quantities of information in a short amount of time. If your processor isn’t fast enough to handle all this data, you might suffer from lag and delays. Obviously, lag is a real killer when you’re gaming.
Some processors allow for overclocking. Overclocking is when your processor operates at a faster speed than what it was programmed for. Hardcore gamers love overclocking because it improves game performance. You can activate overclocking via BIOS. Since we’ve been discussing all things BIOS, we might as well share some overclocking secrets to help you boost your processor speed.
Be warned: overclocking may void your PC’s warranty. It may also cause your computer to overheat, which is why you must pay attention to how hot your computer gets when you’re running intensive programs.
It the heat being ventilated from the computer is very noticeable, you should take a break and turn the computer off for a while so it can cool down. Overheating can damage your interior components.
To activate overclocking on Windows 10:
1. Go to Settings —> Update & Security —> Recovery
2. Under “Advanced Startup,” click “Restart now”
3. Your computer will restart, and it will give you access to BIOS settings when it starts back up
4. You need to change the CPU frequency; depending on your computer, there will be an option for “Cell Menu,” “Ai Tweaker,” “CPU Settings,” “Frequency Controller,” or “MB Intelligent Tweaker. Click whichever one appears on your BIOS settings tab.
5. Click the “Adjust CPU Ratio” option
6. Click on the “Auto” setting and press “Enter”
7. You’ll be given a list of alternate settings; choose a number higher than the existing setting and press “Return”
Again, these settings may look entirely different depending on the computer you’re using. No matter what computer you have, just know that you need to access the settings that allow you to increase your CPU frequency/clock speed. You may need to do some experimenting. Be sure not to push your processor until you know that you adjusted the settings correctly.
Some CPU manufacturers make it easier for you to overclock, and they may include “auto-overclocking” options you can select.
Read this guide on overclocking for more information.

To recap

The CMOS battery powers your laptop’s BIOS firmware, which is responsible for booting up your computer and configuring data flow. You can tell if your CMOS battery has died if your laptop has difficult booting up, if drivers disappear, and if your laptop’s date and time are incorrect.
Replacing a CMOS battery is a very simple fix. Don’t panic if you’re having rebooting troubles. Before you take your computer in for maintenance, get a screwdriver and a new battery and try swapping out the old one. It’s a fast, easy DIY project and could save you lots of money in labor costs.
[1] HowStuffWorks.com; BIOS
[2] ComputerHope.com; CMOS

About the Author

Zach Cabading is a contributing writer for HP® Tech Takes. Zach is a content creation specialist based in Southern California, and creates a variety of content for the tech industry.

Disclosure: Our site may get a share of revenue from the sale of the products featured on this page.