Sorry for. my previous post, I am totally unfamiliar with Isotherm fridges so cannot help you sort out your problem. The fridges certainly look energy efficient and would be something that I may well look at if ever my Dometic reaches it's "best before" date.

I hope that you can work it out, there has to be a simple wiring fault causing a load to be dumped. Can you put a multimeter into the battery circuit and check the discharge ? Is it possible that you have a fault in the solar controller or the pabels themselves ? I am literally,bworking from first principles, probably like you.

Good luck, please come back and tell us - such information is always good to acquire.