I just looked over the 12volt Main Schematic for my 2014/13 Ext body, Rear Lounge Airstream WITH solar. These are the various connections that COULD draw/use electrical power from the RV batteries. All other 12 volt
electrical items are on the other side of the Main Battery Disconnect (the switch on the door frame). If the Master Battery Switch is off, those other items have no ability to access 12 volts from the RV batteries. I do not know the possible wattage draw on these items. I keep it plugged in when I'm not using it.
1. Inverter receives 12v
constantly from RV batteries.
2. BIM (also called Battery Separator)
3. Dash radio is always powered to keep its memory.
4. Solar controller-it probably has some draw as it has an electrical circuit.
5. Tank heaters--only if turned on of course.
6. Rear lounge motor--only if in use to lower/raise the lounge.
7. By-pass engine start push button for Mercedes--only if pushed of course.
8. Master battery disconnect switch--if off then no draw on what is hooked to the main power distribution box.
Per Magnum specs....inverter usually draws 5 watts and NO LOAD 19 watts typical
The BIM-battery separator will charge the Mercedes start battery IF the voltages of the RV batteries are sufficient (don't know the settings) AND the MB engine battery voltages are BELOW a set-point voltage (don't know the settings).
The Carbon Monoxide (C) and Propane (LP) detectors along with the LP tank shut-off valve and the 12v
side of the refrigerator do not receive ANY 12volts with the Master Switch OFF. NOTE: the CO detector does have a 9volt battery internally and it reminds you to turn off the 12v
Master before opening and changing the 9v battery.
The motorized side step, the step alarm, the power awning (if equipped) and the backup camera all are supplied 12volts from the Mercedes engine starting battery.