did you repeat your trouble shooting steps with each battery? perhaps the rebuilt battery is the root of the problem...the part about it working when manually stopping down and firing is baffling.
Yes, both batteries were involved in this test. The rebuild of the backup battery was accelerated because I thought this was a voltage/battery issue. But it looks like something else, I am thinking it might be a contact issue @ the lens/body area or a breakdown of the shutter internally within the lens. Your comments are appreciated.