Charge profile is not linear in existing batteries. A supercharger is 40mn to 80% and 75mn to 100%.

Many people have a mental model of battery charging like a tank of gas or another fluid, in which the first 10% and the last 10% take the same amount of time and effort.

It seems like a better mental model of battery charging would be a pressurized container of a compressible gas: the more you put in, the more it takes to put the next bit in.