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A motherboard is a very technical piece of hardware with many small electronics peppered around it, helping to power and send information to the rest of your computer. However, did you know that the entire board draws power from a simple CR2032 battery (the CMOS battery)?
But what exactly is this CMOS battery, and what does it do? More importantly, if it runs out, how do you replace it?
What Is the CMOS Battery and What Does It Do?
A CMOS (Complementary Metal Oxide Semiconductor) is a chip on your motherboard that stores BIOS information. Since the BIOS handles low-level tasks before your PC boots up and eventually hands the process on to your operating system, it doesn’t get a chance to access your hard drive or SSD.
This means BIOS information like system date and time and hardware settings like voltages, chip speeds, and boot priority are stored on a separate CMOS chip. This chip must also be powered on to prevent this information from being wiped out. On most PCs, the CMOS chip is powered by the CMOS battery, a CR2023 battery similar to those found in watches.
Every time you boot your PC, the BIOS reads the CMOS data and starts the system in its last state. If you make any changes to your BIOS settings, the CMOS chip is overwritten to save this data and ensure that the PC boots with the updated settings.Newer motherboards boot to UEFI instead of BIOS, but that’s essentially the same thing.
The CMOS battery is responsible for making this happen. The CMOS also needs to keep track of the date and time inreal time, so ifthe time on your PC is wrong, chances are you should replace the CMOS battery. Sincethe BIOS needs to be accessed before the computer can boot, the CMOS battery is an absolute necessity.
In fact, not having one can essentially brick your PC, as your motherboard might not boot without it at all. Therefore, it is important to keep an eye out for your motherboard’s CMOS battery. However, they generally last well around a decade or so in one go, so you won’t be swapping them out very often.
Do Laptops Have CMOS Batteries?
Yes, your laptop has a CMOS battery. However, the exact shape and size might differ. Given how compact laptops have become over the years, cramming a full-size CR2023 battery on a laptop motherboard is challenging.
Depending on your laptop and its age, it might have a smaller CMOS battery, usually installed on your motherboard’s non-visible side. This can make replacing the CMOS battery a nightmare, but laptop CMOS batteries are more resilient than their desktop counterparts and likely won’t require replacing over the laptop’s lifespan.
Laptops with integrated batteries might fare differently. Since the battery isn’t expected to be removed unless the laptop is undergoing repair, some manufacturers use the laptop’s battery or a soldered RTC battery for the CMOS.
In any case, while laptops have CMOS batteries, it can be difficult to swap them out. However, they are built to withstand the laptop’s lifetime, so you don’t need to worry about it much.
When to Replace a CMOS Battery
Other than your CMOS battery dying, several other factors might call for a CMOS battery swap. If your CMOS battery is failing, you’ll likely see the following errors pop up during boot:
The “New CPU Installed” error might confuse you, especially if you haven’t changed your CPU since the last boot. Since the BIOS stores all hardware information of your system, if the CMOS battery dies or isn’t working properly, this information is wiped out. This means your motherboard doesn’t remember the CPU and thinks you’re using a new one instead.
That said, most newer motherboards store important information in non-volatile memory. So, if your CMOS battery runs out of juice, your system will, at worst, mess up its time settings. If you’re still using an older motherboard, though, here are some of thebest DDR5 motherboardsto help you upgrade.
A dead CMOS battery can also have the samesigns as a dying motherboard. Replacing or “pulling” the CMOS battery is also a good way of resetting your BIOS to fix issues you might be facing. That’s not to say you should be swapping out your CMOS battery every few months, but swapping it out for a fresh replacement is a good idea when updating components or doing general maintenance.
How to Replace a CMOS Battery
As long as you’re working on your desktop, swapping the CMOS battery is a simple matter of removing the side panel, locating the battery, and swapping it out with a suitable replacement. It’s no different than changing the batteries in your TV remote; just ensure to get the right battery and place it in the right orientation.
However, you should take some security precautions during the process. For starters, power off your PC and unplug it from the wall to avoid static discharge or other residual power frying your motherboard. I also recommended that you note the battery’s orientation to remember how to put the new one back in.
Finally, not all motherboards use a CR2023 CMOS battery. If you’re using a motherboard made for a special requirement or one that is rather small in size, the manufacturer might use another kind of battery. In any case, most, if not all, batteries have their model numbers and relevant information either printed or engraved on them, so finding an alternative is a Google search away.
The CMOS battery is a small but important part of your motherboard that requires attention occasionally. Simply removing and reinserting it can also reset your BIOS, which is a handy way of fixing otherwise difficult-to-diagnose issues. It’s important to be aware of such small things on your PC because, in the end, they make all the difference the next time your PC faces an issue.
