FYI .... make sure all devices have full battery (Drone, Controller, Cell/Tablet) for some reason it checks all, and it has a tendency to fail (with a probability to brick it self) if the Controller or Drone have less than 75%.
For me, the only one that has worked from the start is the manual FW update with putting the zip file (only) , Also it was the only way to update all 3 batteries .