Carbon / Propane Detector Problem

Propane gas detectors, like most “sensor” type devices, have a limited life span and the manufacture’s recommend replacing them every 5 years. Smoke alarms have a manufacture recommended 10 year replacement. I replace mine sooner than 10 years because the trailer is a differ environment than a house. Your house doesn’t go bouncing down the highway nor see as much dust. In California all co2 and smoke alarms come with permanent battery's with no way to replace them other than by a new detector

Welcome.  The one you describe is the LP detector and there isn't one that works from small batteries.  It works by heating a fine wire and that uses too much power.  Even leaving the pod's big battery connected (w/o the pod plugged into your house), it will drain it in less than 2 weeks (the fridge circuitry contributes to this but to a lesser degree).  I replaced the LP detector on my current camper and it is a very easy job.