Why does a laptop say it’s at 6-8% charge, and then it dies, but when it’s at a higher charge, going from 60% to 59% takes a while?
In: Technology
It depends on your settings. Laptops automatically shutdown or hibernate with a certain battery level.
I have mine set to 5% but you can change it to whatever setting you want
It’s because the charge isn’t accurately measured, sometimes even just generated based on average usage. Phones do this heavily, which is why it seems to drain down to nothing for heavy phone users, then sit there at almost nothing for a very long time.
Has to do with battery chemistry and the discharge curve of a Li-ion battery.
Voltage is all you can really read off the battery. The difference between 10 and 20% is a lot of volts, 30 and 60% very few volts, and then 90 and 100 is a lot of volts.
That’s why it drops from 100 -> 70-ish super fast, stays there for a while, then immediately tanks from 25 -> 0
If you click on the battery icon on your laptop, click on more power options, then change plan settings (for whatever plan you want), then advanced power settings. Then under the battery setting you can change what % is considered critical, low, medium, etc… Also what the computer should do at each stage. Could have your laptop force shutdown at 5% or 10% or whatever amount you like.
There are other explanations, but I also know that windows allows you to change the shutdown percentage, I dont know what the minimums and maximums are, but that is ine reason.
Many battery indicators are not well calibrated. Battery monitoring circuits measure the voltage and the current coming from a battery, but do not directly see the amount of charge in the battery.
Software programs estimate that from the voltage and the current measurements, but doing so is somewhat of a black art. Good software algorithms keep records of past performance of the battery to estimate the charge state more accurately, but when a battery can be changed, it may take some time to recalibrate the algorithms.
Laptops (as with other devices) require a certain amount of power to operate, and when they sense the battery is nearly empty, attempt to shut down in an orderly way.
Older batteries may take longer than new batteries to charge up, and may not hold as much charge. Battery charging circuits may push a lot of current into a battery that’s nearly completely discharged, then reduce the current as the battery approaches maximum capacity.
Devices may also measure the temperature of the battery to best charge the battery without damaging it by overheating. (Off topic observation: Tesla cars use battery power to warm the battery itself, as well as a cooling system to keep the batteries from getting too hot.)
beyond saving the your work and getting the machine to a good state, in general a battery that drops below a certain amount of charge, becomes almost impossible to recharge. There are ways to try and bring them back, but it takes certain electrical gear to do it. And most folks don’t have nor really need that kind of gear.
I haven’t seen the actual reason posted yet – it’s because battery characteristics change as they’re cycled, and over time. State of charge is usually determined by measuring the voltage of the battery, but batteries lose capacity over time. In addition, the voltage of a battery going from full to empty is not a linear regression. If you assume full is 5 and empty is 1, for example, the voltage may be at 3.5 at 90%, 3.0 at 30%, 2.5 at 10%, before falling 2.0 at 1%, and 1.0 at 0%.
It’s tough to measure that accurately.
Basically, the closer to 0 that a battery gets, the faster it depletes. Lithium batteries (like in your laptop and cell phone) have pretty flat discharge curves – meaning that they maintain their voltage under load for a long time, but then the voltage drops way off near the end of the charge.
The reason is due to how batteries work. A typical laptop battery has an operating range between 10.1-12.9V. The voltage drops as it discharges and is restored by charging.
The remaining battery capacity is typically figured out from the voltage. So we can say a range of 2.8V each .1V will come out to about 4% of your battery capacity.
However there is more than just voltage at play. Power usage is measured in watts. Watts is equal to the voltage x amperage.
So as your battery discharges the laptop still needs the same amount of power to run. Let’s say your laptop draws 12 watts. So at 12V the laptop will pull 1 amp. At 11V the laptop will now draw about 1.1A. So because the laptop now draws more amps the voltage will drop faster thus causing your percentage to go down faster. Some computer companies know about this and calculate the remaining watt hours of the battery and report the percentage based on that. That is why some computers may have a very even discharge and others may discharge faster at lower percentages.
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