I guess it doesn’t surprise me that some Thor “technicians” install the BIRD any way that is easiest for them. It’s a much shorter wire run from the BIRD to the Trombetta than to the ignition coil. In my case, the “technician” ran the BIRD wire to the coach batteries “somewhere”. I never figured out where, but it was not to the coach batteries so the BIRD never got the correct voice outage from the coach batteries. I fixed it by cutting that wire, adding a fuse, and attaching it to the coach battery side of the Trombetta.
In your case, the BIRD is “hot” all the time. I wonder if that is good for it. On the other hand, I do not see why the BIRD should discharge the chassis battery even hooked up incorrectly. The BIRD only opens and closes the Trombetta and if the Trombetta is open, both battery banks will equalize. If it is closed, then neither battery bank should be affected by the BIRD - especially infrequently.
When I had my problem, I finally called the people at Intellitec and they we very helpful in working me thru my issue and giving me enough courage to just cut the wire and reinstall it. I think you may be at that point. I wonder what if wiring the BIRD directly to the battery Has damaged it somehow. Before I installed a new one (and i’m Not positive that will solve your problem) I would make sure that installing the new one that way is a good idea.