[JRTJH]

Even with the battery cutoff switch in the off position, there are "ghost drains" on the system. Your CO detector, smoke detector, propane detector, backlight on the stereo and possibly other drains may still be connected to the battery. Most RV battery banks will "drain down" over a period of a week to 3 or 4 weeks.

About the only way to stop the drain is to physically remove the battery from the trailer wiring. Most people will disconnect one of the battery leads to do this. Even then, most deep cycle batteries will "self discharge" in time. Usually not within a couple of weeks, but I wouldn't expect to have an adequate charge after a month or more of "just sitting" in an RV.