Refrigerator Repair/Replacement

I would wire the 120v directly to the heating element bypassing the board and other circuitry and run the refer for 24 hrs and see it it cools. If it does your cooling unit is good and your problem is elsewhere an less costly. I would do this test before I took it to a dealer. If you don't do the work yourself the install of a residential refer will be costly also. Estimate the cost for new additional batteries, mounting them and wiring and install costs (do you have room for at least 2 more batteries), a 1-2k sine wave inverter if you don't have one already, removal of the old unit, installing the new one and modifications to make it fit. Then compare the costs for a new residential to a new cooling unit, if close depending on how much dry camping you would like to do then make a decision. Also if you describe in more detail what you mean by your fridge went "belly up" maybe you problem can be more easily diagnosed by someone on this forum.