Why does my laptop say "you have 3 minutes of battery left" when it's really just 1?

[enderlord99]

I was 2 minutes away from finishing my TF2 match when I got an alert saying that I had 3 minutes of battery left. "Okay," I thought to myself "I'll just plug it in right after the match."

Then it shut down a minute later.

[KillianHawkeye]

It's an estimate and I'm guessing it's based on average mundane computer usage, like word processing or browsing the web. Doing anything that uses more computing power, like gaming, probably also uses more literal power (i.e., electricity).

[warty goblin]

Besides being an estimate, most computers try to shut down properly if given the chance, since that prevents damage to the OS. That takes power, so its quite possible the computer saved enough juice to shut itself down.

[ehsanmaster]

It is just an estimate based on your previous usage. And it is not accurate!
It just missed 2 minutes.
Some times my Laptop says I have 30 mins and after 15mins it shuts down

[Manga Shoggoth]

Besides being an estimate, most computers try to shut down properly if given the chance, since that prevents damage to the OS. That takes power, so its quite possible the computer saved enough juice to shut itself down.

I think later versions of windows by default attempt to hibernate rather than shut down.

Although this brings back memories of wiring servers to UPS packs - each pack had a serial port that you wired to the server so that the UPS could give a shutdown warning in time to allow the server to shut down cleanly when the power went.

Depending on circumstances, a UPS used to give about 15 minutes power, so if the power went out on a large system the wisest thing to do was shut down as soon as the UPS kicks in, unless you also had generators in which case the UPS was just there to hold the servers up^* while the generators kicked in^**.

Of course, there was only one serial slot, and I had to wire four servers into the UPS...


^* Don't ask about about power spikes on the switchover...
^** Don't ask about the time the electricians forgot to connect the generators to the UPS...

[Chronos]

It said that because it's really amazingly accurate at estimating its remaining battery life. Determining how much usable energy is left in a battery is a really hard problem, and gets harder as battery technology improves. Being off by only two minutes would have been undreamed-of even a few years ago.

[Rogar Demonblud]

The laptop is also providing itself with a reserve charge for while it's down--the boot up when you start the laptop actually begins drawing on the battery, before it gets active enough to notice that it's plugged in.

[danzibr]

My condolences.

I find it interesting my phone seems to cling onto life when it’s purportedly about to die. That last 1% lasts way longer than any other 1%.

[tyckspoon]

My condolences.

I find it interesting my phone seems to cling onto life when it’s purportedly about to die. That last 1% lasts way longer than any other 1%.

This is similar to the reserve portion most car's fuel gauges are set for, I think, where the 'out of gas/empty' sign goes off while you still have some time to travel - it's intended to try to allow you to reach a gas station before the car goes out on you completely (or failing that give a chance to safely get out of traffic and park.) Your phone's battery estimate may likewise be set to under-estimate how much actual remaining charge time you have when it's that low, in the hopes that seeing that 1% alert will motivate you to find a place to plug in or at least properly exit out of any apps you are running to avoid having them crash out when the battery gives up.

[Rogar Demonblud]

Or exit out of apps to save the battery.

[asda fasda]

Hmm, I've always thought that the reason why this estimate isn't accurate is that the battery degrades over time and use, and I think there is no way of verifying current state of degradation, so even if the estimate time is pretty accurate when the laptop/phone/battery is new after a while it's impossible to accurately calculate that

[Sean Mirrsen]

The reasons for the inaccuracy vary, but it's a combination of actual inaccuracy and various settings for the device.

My laptop, for instance, gives a first warning at 10 minutes, repeats a more urgent warning at 8 minutes, and forcibly goes into sleep with about 5 minutes of power left. The reason it does so, is that the last few minutes of battery power are still used while it's in sleep mode, and it gives you a short window of time to find a place to plug it in. But should you fail to find a place to plug it in within the next ten minutes or so, it will use up the last remaining bit of power to wake up for long enough to properly shut down.

I usually try not to get to the 8 minute warning, and either plug it in immediately if I'm able, or manually shut it down. Since the estimate is not very accurate, it often runs out of power while trying to shut down from sleep mode, which just causes more issues on powering it back up afterwards.