Keep in mind, while charging the car there's a connected DC-DC converter sourcing from main pack supplying the 12v systems. So the 12v battery is not cycling. It's charge state is being floated by the DC converter. Facelift cars have a better 12v design with an added mini DC-DC converter that supplies 12v keep alive systems directly from the main pack even when the car is not charging.
When a plugged in car finishes the charge cycle it disconnects the big DC converter. The old style cars are now on 12v battery duty cycling... but new cars enjoy the mini DC converter (always connected)