What you say is correct. Except: As the AC battery was installed four years after the PV system, I did have to register it separately with the grid operator, wh

What you say is correct. Except: As the AC battery was installed four years after the PV system, I did have to register it separately with the grid operator, which included creating a new entry in the Martstammdatenregister. In other words, registering the PV system and the battery were two completely separate processes for me.