Occam's Razor would suggest that the simplest answer is the correct one, but this never seems to work for motorcycles.
The 4V reading does sound weird. I'm surprised your bike started with the battery reading that low.
You should definitely have a ground under the triple tree - this would mess up dash and lights, but I don't think this would affect battery charging
https://www.buellxb.com/forum/showth...y-and-Solution
Also consider adding an additional ground path from the ignition coil bolt to the frame
https://www.buellxb.com/forum/showth...nding-the-coil
Look up the tests on the stator and voltage regulator / VR. My battery just died, and I'm thinking it's the VR.
Prior to that, I had the hardest time getting the bike to catch on ignition. Initially blamed it on a weak battery. But finally turned out to be the fuel pump, which is another weak link on our Buells. Specifically on mine, the electric fuel pump itself was working but the internal connecting hose had a tiny hole in it, so the pump was essentially just pushing fuel back into the frame.
Lunaticfringe here can get you a good deal on a pump rebuild / replacement.