No one has mentioned it, perhaps it is too obvious but a key difference is that with cars you can use regenerative breaking to convert kinetic energy back to el

No one has mentioned it, perhaps it is too obvious but a key difference is that with cars you can use regenerative breaking to convert kinetic energy back to electrical energy. I don't think ships stop and start nearly as much as cars, I guess a propeller could be used as a regenerative break, I don't think it would add much to the efficiency though.