Head turner:
there is a little lost in the translation between ECD and us ignorant anglofiles!
The battery being physically connected to the electrics system is taken for granted. It is installed and electrically in series with the looming!
Where the confusion came in was whether the alert letter (when it stated battery must be connected) meant the battery must be swithced ON.
I have talked to ECD personally and they say:
Physically plug the external power supply into the a/c first,
THEN switch the BMS on,
THEN switch the ext pwr on.
The battery is there to act as a buffer.