2008 forest river super light

Your DC power supply in the trailer is not working. Check the fuses.

Sounds like it's converter time. Progressive Dynamics makes a drop in replacement unit. Your battery should be vented to the outside btw.

This happened to me too on my 2016 Shadow Cruiser. I'm not an electrical expert, but I assumed it was something (or multiple things) sipping electricity causing a slow drain. My suspicion was that it was something trivial like the powered antenna left on, or who knows what. It would take a week or so, if I remember correctly, before I started hearing the detector beeping too. I fixed it by installing a battery disconnect.

Just curious, how long after a charge does it take for the battery to drain to the point of your carbon monoxide detector to start beeping?

Your converter isn't working. Check the 120V circuit breaker to your converter, make sure it's still plugged in, and check the output of the converter directly at the converter. Should be 13.5V±.