What Happens When Your Motherboard CMOS Battery Is Dead

Do you have a dead motherboard battery? I too have dealt with expired or failed motherboard batteries and know the headaches it can cause.

In this article, I will explain what a motherboard battery is, how it works, issues that can arise due to a faulty or failed battery, and even how to save money and replace it yourself.

Table of Contents

What is a CMOS battery?

The motherboard battery or CMOS (Complementary Metal-Oxide Semiconductor) works as a RTC (Real-Time-Clock) on your motherboard. The CMOS acts as a battery powered semiconductor chip inside your computer that stores important information. This information includes the system time, date, and system hardware settings for your computer to startup and load correctly. All this information is preserved with a near quarter-sized lithium battery located directly on the motherboard of the computer.

What causes a dead CMOS battery?

Corruption of CMOS is unfortunately very common. “The average lifespan of CMOS batteries are 2 to 10 years according to [Zach Cabading contributing writer for HP Tech Takes].” If you use your computer more often the battery will last longer. If you go a long time without using your notebook or computer, the battery is constantly in use preserving all that important startup information.

How to detect a CMOS battery failure:

Computer is refusing to boot the Operating System.
Keeps shutting down without any user input.
Time and date on your computer are constantly wrong.
You are unable to connect to the internet due to an error: “time and date do not match.”
You hear a constant beeping sound.
Printers may not work and display a message “can’t find printer.”
Displays messages such as “Booting Error, unable to detect disk drive.”
CMOS Checksum Error, CMOS Read Error, or CMOS Battery Failure

Troubleshooting the CMOS

To verify that the battery is in fact the issue we will need to narrow it down. To do this, we can reset the CMOS battery. This is actually a very simple task that requires only a couple of screwdrivers. You will need a #2 phillips-head screwdriver to remove the side of the case and a small flat-head screwdriver to remove the actual battery.

Power off and unplug your computer or notebook. Don’t forget to remove the main battery first if you are servicing a notebook.
Remove the screws of the side panel or bottom of the notebook to gain access to the motherboard
Once you open your computer or notebook you should find a small jumper next to the CMOS battery. It should read: “reset CMOS” on the actual motherboard.
Remove the jumper and don’t replace it until after 20 seconds or longer.
Place the jumper back the exact same way it was removed.
Close the computer, plug the cables back in and start your computer or notebook.

If you are still experiencing the same problems, you have now verified that these issues are not due to corrupted settings, and are stemming directly from a faulty or depleted CMOS battery.

If you have a multimeter available, you can even use it to test your CMOS battery. Simply remove the CMOS battery. Set your multimeter to test DC voltage and a good CMOS battery will read over 3.00 Volts. If it is less than 3.00 volts it will not save the information.

Out of curiosity I removed the CMOS battery from my custom-built computer. I had 3.08 volts currently on my battery. I purchased my ASUS motherboard about 2 years ago. These readings may be different for others because I use my computer daily, typically hours at a time.

How to replace the CMOS battery

Now that you have established that you will need a new CMOS battery for your computer or notebook, its time to make your purchase. As a personal preference, if I am not in dire time restraints and willing to wait a few days, I will usually go to Amazon and purchase a two pack with free shipping for less than four dollars. You can visit your nearest electronics, home improvement or superstore and purchase one for a comparable price if you need it faster.

Don’t forget to verify your specific battery type before you make your purchase. Locate this information in your user manual or from the top of the CMOS when opening your case. In my experience I have found it is usually a CR2032. In a pinch I have used a CR2016, but it only has about half the life.

Unplug all cables except for the power.
Unplug the power cable and with the power cable removed press the power button located on the front of the computer or notebook (after removing the notebook main battery) and hold it for about 5 seconds.
Remove the screws from the rear of the computer.
Slide the side panel off the rear of the computer.
Locate the battery. It is a small shiny round battery as seen above.
Remember which direction the battery is installed usually with the writing side/positive side up.
Remove the battery from the motherboard.
Install the new battery in the same socket exactly as the previous battery.
Replace the side panel of the computer.
Install screws and secure side panel.
Re-connect all cables and turn the PC on and set the time.

After your computer boots up, you should see that the time and date settings are saved. Congratulations! You have managed to save your sanity and money by doing this repair all by yourself. Okay, I might have helped a little, but I’m not telling anyone.

How do I get the CMOS out of the motherboard without damaging it?

Use a flat head screwdriver, push the metal tab back away from the battery. It should not take much force, and the battery will just pop out.

Is the CMOS battery the same battery found in Automotive Key Fobs?

Excellent question, YES! The CR2032 can be found in many devices from calculators, wrist watches, medical devices, toys, and many more.

Can a motherboard run without a battery?

Technically, YES. Removing the CMOS battery will allow your computer to run however, you will lose the date and time settings, the computer will boot with default BIOS settings or you will have to choose the drive that the OS is installed every time you start your computer.

Will removing the motherboard battery reset BIOS?

This is an excellent question I get asked alot. The short answer is YES. If you remove the battery, wait approximately 5 minutes and then reconnect the battery.

Can a CMOS battery cause a black screen?

A faulty battery removes all of your boot settings. It is very possible to see nothing but a black screen when booting up a computer with a dead CMOS. For example if you have a secondary video adapter that your monitor is plugged into and your BIOS has reset to default settings, your onboard video would be the new display and not your primary video adapter.