Running a dual battery setup?

I am interested in running a dual battery setup to run a fridge in the back of my car while it's parked. I travel a lot and live out of my car for extended periods. Anyway, if I use a relay/ silonoid to isolate the batteries, I am wondering if when I close the relay on the silonoid if the current draw from the dead battery will be too much for the inverter. I suspect that each night I will discharge the battery to about 30-40% power remaining, so when it comes time to charge it in the morning, I am not sure how much current it's going to pull. I know dead auto batteries can draw 100A after the car is jump started, which I know is too much for the Prius.

Any ideas? Ways to limit the current to the secondary battery? I was thinking of just going with a 20A or 40A relay, but I suspect what might happen is if the second battery tries to draw more current it will just overheat the relay vs actually limit current to the battery.

 

And the answer is?

 

Running dual battery systems is not exactly unheard of. It's quite common actually. I know it can be done, the question is just how. I know if I could limit the current to the second battery somehow, then the inverter would just see the battery as a standard load like the headlights or anything else.