A pair of COSTCO
Automobile starting batteries
Size group 27
You definitely do not need expensive almost deep cycle batteries
Disconnected from shore power a pair of group 27 batteries will do just fine for 500- road-miles powering the refrigerator. But not suitable for say two overnights on the road. A single scrimping night, yes. But no large loads. Three lights max at a time on for no more than three hours.
The batteries will have a multi-year warranty plus Costco's refund "The colors clash" policy. Take the refund and buy Cyclable RV batteries next time.
Engine starting batteries use less water than RV batteries.
They are a deal-maker according to your budget.
