The fridge is a compressor based fridge, a Norcold DE-0061 model. It doesn't use propane, but it will make inroads on your battery's charge.
On the CS, you have three options:
- Buy the "engine generator" option. Caveat with this is that you run into troubles if idling a Sprinter engine for long periods, maybe running the risk of plugging the DPF, which can cost $3000+ to replace.
- Get a propane generator option. This will charge the batteries, but propane generators tend to not have a long run time on the 10 gallon tank. From what I know, you will be able to run the generator 20 hours, tops.
- Getting an external gasoline powered generator. A small, 1000 watt inverter generator can run 8-12 hours in less than a gallon of gasoline, good enough to top off the batteries. However, you will need to find space for that somewhere.