When considering an auxiliary battery or recreational power supply to run your 12 volt accessories and fridges, work out what your needs from a power perspective are first. Rather than ask how long will the power supply run a fridge, understand the load that your fridge at a certain temperature setting will draw. Is it set at minus 15 or at 2 degrees, what are the conditions you will be operating in etc. The basic average draw information is typically addressed in the instructions of most and all accessories. Also consider the voltage range that your fridge will operate between and or the wattage that accessories draw. A basic understanding of your needs allows you to work out what charging speeds you will need by solar or DCDC, and or ACDC.