ARB fridge. Spent last week in Moab and St. George (Hurricane. Oneeeasyrricane) Utah. Was 110* outside. Put tap water in the water jugs, then into the fridge. Fridge would FREEZE the water, running off 12v battery power, yet takes so little juice that the battery didn't even notice. Not cheap, but well worth it. Carried it in the back of the TJ.
I bought a Colman 12v years back works ok but will drain a battery in a few hours easy
But... if it's a wheeling rig, you will run that vehicle for a few hours every day you're out and about. So, it will never drain the battery until you park it in the barn. And in that case, you don't need the fridge running.The ARB units claim just under 1 amp of power draw.
Your typical automotive battery is good for about 40 to 80 amp hours depending on sizing.
So, in theory, a fully charged 80 amp/hour battery should run the cooler for a little over 80 hours.
BUT!
You generally dont want to take a starting battery below 50% of its rating, or you risk harming it. That 80 hours just became 40 hours.
Thats still about 2 days of constant run time on a dedicated battery, but I cant imagine it runs constantly, so maybe 4 days? Toss a couple solar panels on the roof and if they are big enough, you could probably go for a LONG time.
I bought a Colman 12v years back works ok but will drain a battery in a few hours easy