Thanks ST and BPF,
The considered opinion here is that it is probably a charging problem, but in view of the warnings given above, we'll keep her in the hangar and let the mechanic fly to us.
I'll post again when we have an analysis.
due to the stupid design of the starter
I was wondering about that. What's wrong with the good old Bendix gear? Not sophisticated enough? Not enough room to mount a gear ring on the front of the engine?