If you plug your smartphone into your cars usb cable which is part of the stereo system I believe, I guess it’s charging itself whilst plugged in.
Obviously you should not leave it in accessory mode as it will drain overtime.
But what about when running? Is the smartphone draining to the point the alternator can’t replenish etc and so one should not attach phone to car, or is the alternator recharging the battery when running regardless of iPhone use.
Thanks