I've read various threads of how to maintain the 12V battery while my Sept. 2016 S75 sits idle for about seven weeks. Recommendations include trickle chargers and just keeping the car plugged in seem to be common. I'm led to believe the 12V battery takes its power from the main batteries that power the electric motor. If true, can I simply leave it plugged in and set the charge for 70%? I assume the 12V battery will then take whatever it needs, whenever it needs it. Is it more complicated than that? Thanks in advance.