A resistor to drop some of the voltage is definitely a terrible idea, and a more sophisticated solution would probably cost as much as a new and more appropriate controller. Why not just run four "12 volt" batteries, for 48 volts nominal (and over 52 volts at full charge)?
Maybe knowing more about the controller would help - which Kelly Controller model is it?
Maybe knowing more about the controller would help - which Kelly Controller model is it?
