Don't Use The Battery For The Fridge
I have rented boats in this configuration, what I normally do is the following ...1. Get the empty fridge cold by running the engine, this also confirms it is operating correct.2. Place ice in the fridge, not too much, enough to fill 10%-15% of the volume of the fridge.3. Supplement ice with running the fridge with the engine running for an hour in the morning and an hour when motoring to your anchorage. If your not moving the whole hour, keep the engine idling at 1600 rpm for the balance.4. Add ice every forth day.Then your battery usage for the fridge = zero, lots of other uses for the battery. Can't run the engine for the whole hour? ... then your still only using a small portion of your battery each day if you run the fridge for two hours.Note, charging the battery after it passes 85% of full capacity becomes slower, making it very difficult to reach 100% every day, so you really only have about 35%-40% of your AHr rating available to you each day (not 50%)