I use a 130ah battery. I charge it two ways. First way via a 30w solar panel which is on the roof of the car. It attached to the arc pak via anderson plug. If you do it this way make sure you use a regulator with the solar panel so you dont over charge the battery. The 30w panel puts about 1.6amp per hr back into the battery. The fridge uses about 1.5 amps per hr. So it helps to keep the battery topped up. I have also run leads directly from the battery to the back of the cab, where i have set up a 12v socket. If you do it this way make sure you use min 6 guage cable and use attach a 40amp fuse. I then plug in the dc to dc charge into the 12v socket. This charges the battery around 6amps an hr. When i get to a camp site i just use 120w solar panels. I get about 2.5 days out of the battery, if i dont charge it at all. I never let the battery fall below 20%.
If you are going to put a 12v socket in the tub, make sure you connect it to the battery directly. Reason being the nav has a smart alternator, it you connect it any other way the ark pak wont charge. Oh remember the 30w panel does not always put out 1.6amp per hr, it depends on the amount of sunlight, hence why i charge it the two ways. Both set ups cost around $85 ea.