Why Do Motherboards Have Batteries?
In this week’s Tech 911, the reader writes to seek some clarity rather than address a broken device or faulty hardware issue. The said reader was probably poking around with his motherboard a bit and the thought came to him: If my computer is plugged into an outlet, why is there a battery on my motherboard?
Lifehacker SAmore reader writes:
“Could you write a post and explain how I use, what is and why we have a battery on the motherboards? Also important is how to replace it correctly? “
Fast, simple, easy – at least that’s the question. To answer this question, we’ll start with the basics. In some systems, a CMOS battery powers a small, volatile, ultra-low power memory chip on the motherboard. This memory chip is responsible for storing the BIOS settings of the motherboard. If you didn’t have a battery, your motherboard would always boot with factory default BIOS settings – sort of like a Groundhog Day scenario.
The battery powering the CMOS chip also powers the motherboard’s real-time clock or RTC. It is responsible for keeping the motherboard timing accurate and can help you determine when your CMOS battery is dying (or low). If you notice that the times are really wrong during POST, when you open the motherboard BIOS or inside your operating system, chances are good that you need to replace the CMOS battery.
Since in some cases the CMOS chip is responsible for storing your motherboard’s BIOS settings, one simple troubleshooting method you can use when facing a hectic PC that is having problems during startup or POST is to simply pull out the CMOS Battery. This will reset your motherboard’s BIOS settings to default values and, in some cases, can fix any issue you are experiencing.
These issues can also alert you that your CMOS battery is dying (or low). If you find that your motherboard settings keep resetting to defaults, or you are having trouble booting your operating system (or even finding hard drives), it might be worth looking into a new CMOS battery if several years have passed since then. ever since you bought or assembled your computer.
For newer PCs that store BIOS settings in non-volatile memory, the only indication that something is wrong with the CMOS battery might be a small error message when booting the system (or the timing will be completely wrong). You can still remove the battery to reset BIOS settings. Although the CMOS battery is not directly required to store these settings in memory, your motherboard may see the missing battery and say, “Oh, I have to reset all settings to factory defaults like in the old days.” Your motherboard may also have a completely different procedure for resetting BIOS settings to defaults – it’s best to consult your manual on this matter.
The lifespan of a CMOS battery depends on its total capacity, the amperage your motherboard draws, and how often you use your system. A good rule of thumb is to consider replacing the CMOS after about three years or so. (This is “think about it in case your computer starts acting weird and you don’t know why.” You don’t have to go out and accumulate battery for no reason.)
Your battery can extend its life by another five years or more. As a general rule, I don’t worry about the battery until it looks like it’s dead. Since watch batteries are cheap, going to the store for a new battery is a bit of a nuisance if (or when) your computer has mysterious BIOS issues.
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