Whether it’s a low battery or a faulty battery, Windows a good job alerting you to laptop battery issues. But how exactly does it detect problems? Read on as we investigate.

Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.

The Question

SuperUser reader Cam Jackson is curious how his Windows 7 laptop knows the battery is going bad:

I have a laptop that’s a little over 5 years old, and I’ve never changed the battery, so I believe Windows 7 when it tells me “there is a problem with your battery”, and to consider replacing it.

My question is: how does it detect a dodgy battery? Does the battery not have the same voltage that it used to?

How indeed?

The Answers

SuperUser contributor Tonny explains:

Laptop batteries have a small chip inside that controls/monitors the charging process and also monitors the number of charge/recharge cycles.

This chip is factory programmed with information how this sort of battery typically degrades over time.

It also can derive information from the charging cycle itself: The time it takes to reach full-charge at a given voltage/current changes when the battery gets worn out.

(Voltage drop during discharge is not reliable as it depends a lot on the amount of current drawn while discharging, so it varies with the use-pattern of the laptop.)

Windows communicates with this chip to get information about the battery health.

Have something to add to the explanation? Sound off in the the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.

Jason Fitzpatrick Jason Fitzpatrick
Jason Fitzpatrick is the Editor in Chief of LifeSavvy, How-To Geek's sister site focused life hacks, tips, and tricks. He has over a decade of experience in publishing and has authored thousands of articles at Review Geek, How-To Geek, and Lifehacker. Jason served as Lifehacker's Weekend Editor before he joined How-To Geek.
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