LP Gas detector.

[dnskuster]

The PL gas detector has lost power and I can't find the fuse for it.

 

[Mr. Dan]

Some are in line in the wall behind it.
Some are fused near the battery or so I’ve read.

 

[RhumbleFish]

Not sure of your rig, or if you have the 2017 Cardinal 3250RL. LP Detectors are almost never run through the fusebox.

Cardinal actually has a decent electrical schematic/writeup available (though it's old and likely not applicable). Still, if they published this, they might also have published one for your 2017, or are availlable to call/email and ask.

In the meantime, this thread might help:

https://www.forestriverforums.com/forums/f22/propane-leak-detector-fuse-location-235971.html

The OP found his LP detector to be run through one of three 3amp fuses found at the battery.

Mr Dan is also correct, many have also found a fuse immediately behind the detector.

Just my .02, hope this helps.