One further point on the 24v issue.
I have seen the voltage drop from 25.4v to 24v during the time it takes to complete the cockpit pre start checks, once the voltage dropped to 20 volts and the GPU was connected, then switched on for the start.
Surely the minumum voltage for starting ought to be stated both in the Limitations section and in the pre start check list prior to putting engine switch to ground idle.
And instructions for disconnecting the GPU.
Failing any instructions we run both engines up to ground idle , with the BMS on. When both engines are stabilised at GI we disconnect the GPU, by switching off the GPU then removing the plug from the a/c.