Main Battery Low voltage

I'm having an electrical problem the Sport 912iS engine, #441 7198, in my 2016 Tecnam Astore microlight aircraft.  The engine appears to be delivering some charge in cruise but not sufficient to supply all the 9A load and recharge the main battery. i.e Last flight, voltage read from Dynon screen: Pre-engine start 12.1V, post engine warm-up 12.5V and at cruise after 1hour flight 11.9V.

Since new the annual inspection reports show the voltage ranging between 14V - 13.1V. However, in the two years I’ve owned the aircraft I’ve never seen the voltage above 12.7V and the problem appears to be getting progressively worse. I’ve not added any addition load to the system. I've replaced the battery with a like for like HC20 Fullriver 12V 680PCA but I didn't see any improvement. I now must connect up a battery recharger after each flight.

Lanes A & B typically display 14V – 13.9V.

In Feb 2024, with the engine at 4,000rpm and all electrical loads ON, I’ve taken voltage readings at the battery terminals 12.8V, cigarette light socket (bus) 12.9V and the Dynon screen12.6V @ 9A. This would indicate that the connections are good, no dry joints, etc and that the voltage displayed on the Dynon screen is a good representation. I’ve traced the wiring and found no loose connections. Refer to the attached for voltage readings I've taken over the last year.

 I’ve been in contact with my local Rotax agent, but he is as baffled as I am. He did say he’s more familiar with carbureted 912’s than the injected electrical system and I got the impression he was too busy to spend the time investigating the problem.

Any advice on how to diagnose this problem would be most appreciated. Does this sound like a problem with the Regulator B, Alternator B or Stator B? I have access to an oscilloscope. Are you able to provide me with a procedure on how best to take the readings and what pattern and numbers I should be seeing?