Originally Posted by KIX
12 volt reefer operation is not a popular choice because of the 12 volt load. As an example....if your reefer has only one electric heater it probably uses about 225 watts to operate it. When using 110 volts you would use about 2 amps.......when using 12 volts for the same amount of wattage you would use approx 18.5 amps from your battery pack. So, the short answer is 12 vdc operation uses too much of your available battery capacity. And, propane uses almost none of your battery capacity.
The only thing is if you are running down the road your alternator is powering your frig through the batteries. If you shutdown the engine then you are using up your batteries. If you have a heavy duty alternator like probably most do you won't use any battery power. Mine is an 86 and it came with a heavy duty which I'm thinking is either 85 or 100 amp. That's more than enough to run your frig and still charge your batteries while driving. And I also have a 3way.