> A car battery should be swappable in a day or two

Nio currently swaps out their car batteries in about 3 minutes, much like you'd get an oil change at Jiffy Lube or something. It's completely automated except someone pulls the car in/out of the bay for you. I imagine that human step will be relatively short lived.

> they have to be heavily shielded in case of an accident.

Yes, it's just a simple matter of purposefully designing it to be removed easily.

This is cued up to where he gets to the battery swap station: https://youtu.be/hTsrDpsYHrw?t=358