It is common in Airstreams, and maybe in other trailers, that the propane detector is wired directly to the battery. My propane detector manual says that it should not be disconnected from the battery or deposits will build up on the sensor and cause false alarms for a significant period of time when power is re-applied. I have not observed this.
My CO detector is operated with an internal battery, like home smoke detectors, but I don't know about yours.
Assuming you have a single fully charged Group 24 battery (which has around 85 amp-hours of capacity) and assuming only your propane detector is drawing current, the battery will be exhausted in 50 days or less. If you also have a CO detector operating from the trailer battery or any other parasitic loads, the time will be shorter.
Your experience may, in fact, be normal. I rewired my propane detector so it would be off when the STORE/USE switch was put in the STORE position.
"You cannot reason someone out of a position they have not been reasoned into"
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