Most RV fridges are designed to operate using propane and electricity and sometimes the coach battery.  Two way fridges generally run on propane when the RV is not plugged into shore power and automatically switch to run on electricity if an external power source is detected.  Three way fridges are able to operate using propane, electricity or the coach battery.   Most of our RVs are two way.   The exception to this is in our 2022 Forester units and in our Coachmen DVC units where some models operate off the coach battery only.  When plugged into electricity, 12v fridges continue to run off the coach battery which is being charged by the shore power hookup.  Please check the How to Guide and the Guest Guide for the model of RV you receive to confirm the required settings for the refrigerator.