starting to lean towards faulty fridge - now I am a bit concerned as I have only had mine a couple of months now and it would be a pita if it craps itself whilst settled at a camp site with a few coldies on the go, please let us know the out come.... all the batteries you have tried did you clamp directly on them with the lead to socket ? because I have only ran mine as mentioned with 6mm cable from socket to battery and the car has been upgraded with 6mm cable dedicated power from socket straight to battery... you may still have issues with cable size from fridge plug to any of the batteries that you tried