I remember in movies about old times, you would arrive with your horse-powered cart at a such station, they changed the horses, and off you go. I guess this is

I remember in movies about old times, you would arrive with your horse-powered cart at a such station, they changed the horses, and off you go. I guess this is similar. Make batteries standard shape and size, just the power may vary. After all, the gasoline/diesel is the same all over the world and is made after some international standards. I think we are looking wrongly at the energy source of an electric car. If we assume electric power as raw oil, then the battery is a refinement of this electric power in form of an chemical power. Then in this case the unit of "power" is not the electricity but the battery holding the power to run the car. If you look from this angle, then the battery is obviously the unit that you need to load/unload from the "gas" station.