Possibly stupid question. Instead of charging 1 battery slowly, why can't we charge 50 little batteries in parallel and connect them all back together after?
The problem is that the speed at which you can charge a battery without damaging it is proportional to its capacity. Charging 500 small batteries at the same time would be fine, but in general you’d have to charge them each at 1/500 the speed of the entire pack (in terms of kWh of storage).
The other problem is having enough sheer power available to charge all of the batteries (together or apart) at their maximum safe rate. The new supercharger can apply roughly double the power to the car, which cuts charging time almost in half.