First off plug in the trailer and then turn on the frig to electric. It will take up to 24 hours for it to cool to temp. you should see a difference at about 4 or 5. Turn the propane on and after the frig is to temp switch it to gas and see if it maintains the temp. Batteries won't matter if you are plugged in and during that process your converter/charger will charge the batteries. If you unplug then the 12 volt takes over and your frig may automatically turn to gas or you may have to move the switch. After you have done that and it doesn't work get back to us and give us make and model of frig and we can give specific information to help. A sticker on the door should give you the information.