I would be very surprised if there wasn't a breaker for the fridge
According to a user manual I found online, there should be a breaker for the refrigerator on the DC panel in the head. It may be the breaker below the one labelled shower sump. In addition, you should look up the fridge documentation. Many models have circuitry that will automatically disconnect DC power when the battery voltage drops below a certain level. That keeps the battery from being completely run down. I mention this because if your fridge is protected and working correctly , then possibly something else is killing the battery.