I don’t know if this will help anyone else, maybe its too obscure, but I wanted to post it just in case. I have 4 ESCs connected to the servo control board, and what I figured out finally, is that they each have their own BEC. So even though I thought the power supply to the control board was isolated from the other batteries, they were connected since these BECs were supplying power back to the board through the servo control connectors.
Once I turned off all the BECs on the ESCs, then finally the system would run reliably off of battery power.
I am not sure why when you plug in USB power to the Panda II from a plugged in computer that it works, and all other arrangements fail. Maybe someone on the forum can explain that.
So why does it fail with the BECs turned on? I read that if you want to run off the BEC then you should only ever have one BEC turned on. So if you are running multiple ESCs, you only have the BEC turned on on one of them, and OFF on all the others.
I haven’t tried that yet. I will try it since it would eliminate having the second battery, but it also could be that the other system is glitching the system when it is under load, and a separate battery is needed to keep the power to the Panda II clean.