On hybrid multirotor I tryed to make the fuel level sensor working setting BATT2_TYPE to 24 “analog fuel level sensor” seting all the parameters as explained on the arducopter wiki, but this no work.
I just tested Copter 4.3.3 and master branch Copter. Everything is working on my side. One guess without a dataflash log is you have 2 battery monitors using the same ADC pin.
The dataflash log will have more details about your set up. If you would like to share it privately, you may.