My understanding is you Power the battery on to ‘liven’ MPPT controller before you power switch on the Solar and opposite when removing solar/battery power
If this is not done then the Solar can ‘spike’ the MPPT and cause the MPPT controller to have a major meltdown/failure correct?
So if the MPPT is connected to a Battery with inbuilt BMS and that switches off the battery output if voltage is low SAY Solar charging by day and Battery discharges during the night, then won’t the Solar the next day destroy the MPPT if there is effectively no battery connected?
No. A Victron MPPT will not meltdown. Many people would be in trouble if that was the case. The sequence you list is correct and is meant to allow the logic of the MPPT to power up and detect the battery voltage. Once this is done, if the battery connection is ever lost the MPPT will can remain powered by PV. You are fine.
The “Battery Voltage Check” function is only active the first time the system is started after installation.
After that, the controller remains at the set voltage. The function can be re-enabled for remote installation, but this has to be done deliberately (a pre-configured device is to be delivered to a construction site and installed by trained or non-specialist personnel).