The fridge should be connected to the RV house batteries
not the engine battery
Be sure you have the fridge set to gas aka l.p. not automatic
Most fridge's now are only two way, but a few three way using dc power do exist, and that mode really sucks power
Fridge should need very little power just for control board and gas valve, any battery that can't last days in that mode is bad
What is your RV and what is the make and model of the fridge
PS: we always called it Pre-cooling the fridge
never heard it called priming, it does take time for an absorption fridge to cool, as much as 24 hrs, although 12 will usually be enough
