I have a 2018 Thor Synergy on a 3500 Mercedes chassis. When the motorhome is not in use, I store it in a covered storage area without access to 110 V. If I pull in to storage with the battery fully charged, i.e. 13.2 volts, it will take roughly 5 to 6 days in storage and the battery will be below 12 volts. My only way to charge it has been to start the coach Onan generator and charge the chassis battery with a small 6 amp charger. This of course takes propane, time, much patience and adds lots of hours to the generator. After following some of the forums, I have ordered a 18 W solar panel/trickle battery charger today from Amazon. I live in southern Arizona so I have lots of sun to charge the battery with. The afternoon sun shines in on the front of the cab even though it is undercover and it will provide adequate sunlight on the solar panel to keep this battery charged. I had never thought about the recommendation of putting in a couple of knife switches that was mentioned above; thatís not a bad idea either. After owning this rig for about 17 months, Iíve found that this parasitic drain is common, and did not surprise the Mercedes service advisor when I ask him about it. I guess itís just something that we will have to live with, be that through adding some sort of trickle charger while the coach sets idol, or put on the knife switches and disconnect the power totally. I suppose this is a small price to pay for, in my opinion, an excellent chassis, particularly this Mercedes diesel.