[BiggarView]

ON question 1.... How long you can run on 2 12volt batteries entirely depends on the store capacity of those batteries (20 hour AH rating).

18cu ft Residential fridges uses about 140AH per day. You can do the math for the hours you need battery power. To avoid shortening your battery life (non Lithium) you'll need about double that number of AmpHours. For example if you use the 8 hr number you mention, your fridge will use about 50AH. So you should have about 100AH of battery capacity (use the 20hour AH rating supplied by the battery mfr.) to avoid harming the battery life. We are only discussing the fridge mind you and only for the time you will be towing. Less than that battery size amounts to battery early death. How you use your rig really determine what else you need battery power for.

On question 2...Unless your truck and rig are specifically wired up to charge your rig batteries from the truck while towing... then none.