JoTePOWER

Thanks a lot. The update was successful. And the battery behavior > 90% SOC has improved significantly.

before update

after update
 

The partial schematic of the Axpert MAX family (7.2/8/10/11 ,OGx) below shows the relationship between GRID IN Neutral AC OUT Neutral and Earth. The blue routes are neutrals. Notice the relay 3 ( contacts RLY3A and RLY3B) .  There are 2 changeover contacts in parallel in order to share the load current requirements of the output neutral. 

The relay is energized by the DSP controller when the  machine is in LINE mode (e.g. Grid available and SUB/USB nominated as output source priority )
The wiper of each contact is connected to the load output neutral. The normally open contact is made when in line mode , and ensures the grid neutral is passed thru to the load neutral. When you have load shedding , grid falls away , machine is now in BATTERY MODE (islanding) ,  this relay drops and the normally close contact anchors the load neutral to earth as can be seen.
Please note that this internal bonding is NOT available on older machines , only generations 3 and 4 (eg MKSIII , MKSIV etc).
The arrangement is optimum as the changeover action of the relay is break before make. Such is its simplicity and gracefulness that my own MAX has an RCD grid bound as well as RCD  load bound . The grid bound RCD is not fuzzed by the changeover action of the relay when grid is restored.