Ours has always been sitting outside not plugged in and the battery is always topped off nicely year round by the solar panel, there are a few times I left the trailer light on for a few days and that doesn't seem to have changed anything. I only plug it in before the trip to get the fridge to cool faster.
Our trailer gets about 1-2 hours of sun in the winter (a little more during the summer) sitting at the side yard w/ shade, I noticed even if I covered it the battery still gets charged somehow.
Battery ? with solar. If trailer with solar is stored inside with no power or sunlight, will the controller drain the batteries over time? My understanding is controller doesn't go through battery cut-off switch. thanks