After starting the engine the car battery gets charged and then just hangs out doing nothing. Starting the engine is quick, doesn't draw the battery down much and it really takes no time or power at all to charge it back to its original state. The alternator runs all of the on board demands.
An RV battery may lose 20 to 50 percent of its charge so charging takes more power and time and also requires a more sophisticated pattern of voltage or amps or power.
Converters and chargers normally have more than one stage and most of them have three.
Do we need a physics professor or battery technician to verify that?
The worst way...?
Taking into account the cost of fuel, time, noise, heat, etc. Yeah, it could be the "worst" way.
I love an Old Man and an Old Coot!!