Well, if you think it’s a good idea to keep a spare Tesla battery in the garage that’s cool. Should only take several hours and a complete auto shop with specialized tools to change it.
They aren’t 12 volts, those cars. More like 200VDC. DC is far more dangerous than the same voltage of AC. Messing with them will kill you quite quickly.
I guess someone could have a 5KW gas or diesel generator. But even then it will take hours to charge the car.
Actually I think it’s 400 volts.