before you buy the battery you could use jumper cables from your tow vehicle to the rv battery to see if that is what is needed. check the polarity on the cables carefully don't hook it up wrong! the startup current on the refrigerator will be high to get it started. what size battery cables are you using to hook the inverter to the batteries and how long are they? if they are not big enough the inverter will trip out on low voltage. the inverter will draw over 100 amps from the batteries when the refrigerator starts up. inverter should be as close to the batteries as possible. once you get it working test how long it will run before your batteries run out plug in a old dial type clock and you could tell how long it ran.