The user manual for my RMD8555 refrigerator says that when it is in automatic mode it looks for a power source in the following order:
1. 12V solar
2. 120V line voltage
4. 12V battery
I don't have the manual with me right now so I may have the order mixed up, but my point is that the fridge can distinguish between 12V solar power and 12V battery power. How does this happen? Is it determined by the solar controller in a solar panel system or something else?
There may already be a thread on this. If so, I searched and didn't find it.
The solar and 12v sense lines are not hooked up by ETI. If I recall correctly it was deemed not to be in your interests for the fridge to run off battery without you deciding to do so. Hence it's manual selection only for 12v. The lugs exist if you wanted to get rambunctious and try it out.
I believe it's solar, 12v battery, 120vac, then propane, if they were hooked up.