Am I right in saying that running a 12V fridge in a vehicle is only possible in statioary vehicles when there is a secondary battery installed to run it? Otherwise it would drain the primary battery fairly quickly? I am looking for weekend outings off grid (camping) and need to keep things cool, but do want to bother with complicated battery setups in a normal car (not kombio, not 4x4).

Urgent responses appreciated as I am looking at some fridge specials.