I have the same issue on my Rad Rover 3 years old. Was out riding and suddenly went dead. Battery was in full bars just prior .  Display is blank; lights don't work . Throttle is dead . Test voltage on battery and got 54 volts . Test voltage on output cable of battery tray and got 54 volts . Intersestingly and unexplained is I get 40 volts at same location ( base of battery two outer pins)  with key turned off

Contacted RAD . They sold me a new controller. Put that in . no change. I have disconnected and reconnected all harness commections . No visible damage. Bike always stored inside . Never gotten really wet ( slight rain conditions occasionally )