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 squeezing a strong spring. It’s kinda hard to get started, but once it’s going it’s fairly smooth until you reach the end of the compression, when it becomes the hardest to compress further. That’s charging your battery.