Why is it that mobile phones these days promises to charge your phone up to 80 % in like half and hour.. but it takes another 20 minutes to charge to 100%? Why can’t it just go all the way?

Question

Same with electric cars… I always see “fast charge you car up to 80 percent or so in X amount of time but the rest is not fast?

In: Engineering

Answer 1

imagine you’re trying to fill one of those ice cube trays for your freezer.

you start out by just randomly pouring as much water as you can in the general direction of each cube.

once they’re all *mostly* full, you reduce the amount of water you’re pouring in, and direct it to a single cube. when that one’s full, you move to the next cube, and so on, till each cube is full.

instead of Cubes in an Ice Cube tray, you’re now charging cells in a multi cell battery.

you know that because of the way the cells discharge, they’re all going to discharge *more or less* evenly, so you know that you can fast charge all of them at more or less the same rate.. but, once you get to 80-85%, you have to stop fast charging, and then check the charge of each cell, and just top it up, to prevent overcharging.