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
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.
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.)
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.
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.
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
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.
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
Don’t forget that it’s an estimate, this information is provided to you by the chip in the battery itself (in most, if not all, modern laptops), then further processed by the operating system. The battery (chip) can be calibrated to provide more accurate information, this is often done in the factory, but over time, as you use the battery, that initial calibration information becomes less useful because the battery degrades.
Your operating system also further processes that battery information and tries to estimate how long the battery will last on the current load, however, it can’t predict what you’re going to do next, whether you’re going to close all the applications or open something that requires lots of power.
Lastly, it’s unhealthy for batteries to completely run out of charge, so what you see isn’t the true battery charge level, so the operating system and your motherboard will usually try to protect the battery and kill your laptop before the battery itself fully runs out of charge.
I’m not an engineer, but there’s the whole issue with voltages, which further contributes to the problem.
N.B. a lot of this is based on my own experience, my computer science degree and some quick research, please forgive any inaccuracies.
Batteries aren’t perfect in the way they charge and discharge. Lithium batteries, like the ones in almost all portable devices, are very delicate, and require special care in order to charge and discharge properly. Your phone never fully discharges, because if a lithium battery fully discharges it will never charge again because something inside the battery changes chemically. Your phone or laptop is constantly monitoring the exact voltage of your battery, and the voltage tends to be more consistent when the battery is above 10-15%, but when it drops below that, the voltage becomes inconsistent and often dips below and above the acceptable range, causing the software to shut off your computer
Batteries don’t drain evenly. They drop off more quickly as they get more empty. Lithium cells are actually pretty good about staying flat and even throughout the discharge curve compared to old technology like alkaline or NiCad battery cells. But after your battery gets old, it really starts to drop off more dramatically. That explains what you’re experiencing.
Also, picture a scale. Power on one side, which is what the phone requires. On the other side of the scale, you have voltage blocks and current blocks. The voltage and current blocks are the same weight. Now let’s say 10 blocks is what it takes to balance the scale. If you remove 2 voltage blocks (meaning the battery is draining), you have to add two current blocks to keep the scale balanced. Well the problem is, current output drops as the battery gets closer to empty, and at a certain point, the battery cells just can’t put out enough current to meet the power requirements and it’ll just shut off. (in this analogy, it’s like running out of current blocks to swap for the draining voltage blocks, so you can no longer balance the scale, which is our equivalent to powering your device) This balancing act is what voltage regulators do.
[https://batteryuniversity.com/learn/article/discharge_characteristics_li](https://batteryuniversity.com/learn/article/discharge_characteristics_li)
^ this link has graphs where you can visually see what I’m talking about. If you scroll down a ways to the bottom you’ll see where they show older cells that really drop off dramatically as they near empty.
Also, worth noting that battery cells aren’t zero volts when they’re empty. Lithium ion cells are 3.8 volts, roughly, when empty. And when they’re full, they’re at about 4.2 volts. Going above 4.2 voltage will permanently damage the cell and can cause it to explode. Going below 3.7 volts can also cause permanent damage and most chargers won’t even attempt to charge it. (lithium fires are crazy, so chargers and voltage regulators for lithium batteries are pretty picky about battery health before they’ll attempt to charge them)
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