Why Do Motherboards Have Batteries?

If your computer is plugged in all the times, then why does it need a battery? Turns out, there's a very good reason.

Photo: Rafael Pol (Unsplash)

In some systems, the CMOS battery powers a small, super-low-power volatile memory chip on your motherboard. This memory chip is responsible for holding on to your motherboard's BIOS settings. If you didn't have a battery, your motherboard would always boot with its factory-default BIOS settings — a Groundhog Day scenario of-sorts.

Photo: Amazon

The battery that powers the CMOS chip also powers the motherboard's real-time clock, or RTC. That's responsible for the motherboard keeping accurate time, and can help you figure out when your CMOS battery is dying (or dead). If you notice that the time is really wrong during POST, when you pull up your motherboard's BIOS, or within your operating system, odds are good that you need to replace the CMOS battery.

Since the CMOS chip is responsible for holding on to your motherboard's BIOS settings in some cases, one of the easier troubleshooting techniques you can take, when confronted with a fussy PC that's having issues during the startup or POST process, is to just pop out the CMOS battery. This will reset the settings of your motherboard's BIOS to default and might, in some cases, fix whatever issue it was that you were having.

These issues can also alert you that your CMOS battery is dying (or dead). If you find that your motherboard's settings keep resetting to their defaults, or you're having trouble booting into your operating system (or even finding hard drives), it might be worth looking into a new CMOS battery if it's been a few years since you've purchased or built your PC.

For newer PCs that store BIOS settings in non-volatile memory, your only clue that something is wrong with the CMOS battery might be a little error message when your system boots (or the time will be completely wrong). You can still remove the battery to reset your BIOS settings.

Though the CMOS battery isn't directly required to keep these settings preserved in memory, your motherboard might see the missing battery and go, "Oh, I should reset all the settings to their factory defaults, just like the old days." Your motherboard might also have a completely different procedure for resetting its BIOS settings to their defaults — best to consult the manual on this one.

Your CMOS battery's lifespan depends on its overall capacity, how much current your motherboard draws, and how often you use your system. A good rule of thumb is to start pondering a CMOS replacement right around the three-year mark or so. (That's "thinking about it in case your computer starts acting weird and you aren't sure why." You don't need to go out and stockpile a battery for no reason.)

Your battery might be able to make it even longer — five years or more. Generally, I don't worry about the battery until it looks like it's dead. Since watch batteries are cheap, it's just a slight inconvenience to go to the store to pick a new one up if (or when) a computer starts having mysterious BIOS-related issues.


Comments

    On modern boards it powers the RTC (real time clock) something's got to keep the clock and calender ticking over when tour systems off.

    Since watch batteries are cheap, it's just a slight inconvenience to go to the store to pick a new one up if (or when) a computer starts having mysterious BIOS-related issues.

    Unless you're like me and you get a motherboard in the Asus RoG Maximus range. They're covered in heatsinks, ostensibly to help dissipate heat better and extend the life span of the mobo components. They also provide extra stability reducing flex and the risk of breaking components. Which would be fine if they didn't place the battery smack under one of the heatsinks.

    You need to literally remove the mobo from the case. Which obviously also involves removing video card(s), the CPU and other peripherals so you can unscrew the heatsinks. All to replace a $3 battery. While I appreciate the goal of the heat sinks the design is a pain :(

    https://www.asus.com/Motherboards/MAXIMUS_VI_FORMULA/gallery/

      Its a painful procedure. But provided the Manufacturer has installed a good quality battery you wont need to change it for 10+ years if not more.

      Ive had my motherboard for more than a decade. Never had to change the battery.

        I had to replace mine after maybe three and a half years. Which is disappointing since it (was) the high end Asus mobo that cost a fortune. If they skimped on a $3 battery that's just sad :(

          I have a decades old Gigabyte p55a UD4P and i have not had to replace the CMOS battery since purchase. Guess Gigabyte puts more effort into it lol.

            Which is ironic because I've had problems with Gigabyte quality control on their mobos and vid cards which saw me blacklist them for a decade when buying gear. Leaking capacitors, random hardware failures, and lots of failures *just* outside of warranty.

            I guess though, they don't manufacture the batteries ;)

        Lol.

        Did i trigger you that much @soals that you resorted to going through my old comments just to downvote me?

    ... and then you get tech black magic like my vintage Compaq Deskpro 5100, built in 1996, with the original battery soldered to the mobo. Still working. The clock was close enough to correct when I plugged it in after spending several years in storage.

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