FLA deep cycle battery? You tested/checked for the easy stuff first like bad cell(s), low water, dirty posts etc?
Would running generator overnight 10 plus hours suffice? I am on assignment and don’t have access to shore power while boondockingI really am getting frustrated!!! I wish you were the only one that won't read anything about battery charging. Running a generator for 2 hours won't charge a battery enough to troubleshoot a system. Nor will a trip to your job site. You are simply destroying your new battery.
At this stage an overnight charge is needed to even start troubleshooting your system, and to potentially save your battery.
Something is on, or your converter/charger has a bad diode, but that diagnosis has a high probability of being bogus without a full charged battery. Are all the fuses removed so to eliminate a short in the system down stream of the fuse block?