Did you understand what it means to exchange more than one car quickly?

The problem is not making batteries exchangeable, not problem is making economical.

Lets play a numbers game. Lets assume you want to exchange 5 car batteries per hour? How fast do you need to charge them and how many do you need minimum?

Now 5 cars isn't even fast, you would want to actually exchange them faster to have a real advantage over fast chargers.

If you want to do more cars per hour but charge them significantly slower you have to store more batteries.. so half the speed, double the numbers.. but that ain't even slow.. slow would be maybe ten times slower so ten times the batteries.

Yep.. read it.. a number of time even before you wrote it.