Sfli
I see that you know your stuff.
So you disconnected 30 cell string 4 times.
You probably know that every time you disconnected you reset PIC chip on top board/can call it computer or processing board/ or we should think so. .
I also disconnected 30 cell string several times and after connecting back I had several instances that system didn't react to power button press.
Reason? Bouncing connection.
Simply you must make sure that connect ONLY once , no bouncing.
So you press ring connector, hold it firm , insert Allen key and turn until tight with NO bouncing.
PIC chip has several types of resets. But when you bounce connection it becomes confused.
So try it again.
IF you did not cause obvious short like spark, you NMH electronics should be fine.
Just try again.
I must say that it should be very difficult to troubleshoot top board.
When you top board is "done", you would have to buy used hub from Rick Ruggiero who still services Epluses.
But it is I would imagine $500 for used hub.
For new he wanted $1000.
Unless you are really electronic tech with rework station and tons of experience.
EMS designed those electronics really well. State of art I must say, how else those 30 cell strings would last that long?