We have a 2020 3901. The Xantrex 1500 sine wave inverter is not switching over to battery upon loss of shore power. I'm fairly familiar with inverters having 25 years of owning houseboats. Typically the inverter wont invert if there is no load. Is it possible that the fridge is not plugged into the correct outlet. The fridge only comes on with shore power. Anyone else have/had this issue?