I'll generally use AC, and not even turn the LP on until I'm getting ready to roll.
Plug her in, press the "use" side of the battery kill switch
and that way the batteries get a top off, the fridge cools down, I can fire up the AC while loading clothes and such, etc....
Often though, i don't precool it at all.... or only for an hour or two.
It doesn't take too long for the cooling coil to start getting cool.... which is about all it will ever do anyway. The rest is just cooling down the box, and filling the box full of cold stuff just accelerates the process.....
kinda like the difference between putting one little ice cube in a large cooler vs filling it with ice and water.
Many folks will say the LP is more efficient and will cool faster. Seems plausible, but on a modern, new fridge that's working properly I doubt if you could tell unless temps are extreme &/or you put a stop watch on it.
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