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

The charge flows to the positive charged plate (cathode) of the battery to be stored. The charge is positive and naturally wants to flow away from the positive charged cathode.

Getting positive charge is easier to do when it is empty. Once the charger reaches ~80% the positive charge increases enough to push back on the flow of additional charge entering. It still will fill, but at a slower and slower rate.