I have a 2010 Cougar 276RLS with two 12 volt batteries that will discharge in two or three days if I am running the frig on gas. This is just setting with no other use such as lights, pump, slide etc...
Smoke detector and CO detector will draw a batter down. I disconnected mine in favor of AAA battery powered ones. I boondock extensively. The AAA's will last 2-3 years if you take them out when not using the camper. If you leave them in they need to be replaced once per year.