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?

Question

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

Answer 1

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)