You might be able to keep the motor, but without info from X-treme's tech (not one of the CSR phone folks) it's a risk. Yes, the controller would need to be changed. The last X-treme ebike we worked on had markings on the controller indicating 24V only. Usually if a controller is rated for multiple Voltages that's clearly labeled on the electronics. Wonder about that battery...its awfully inexpensive. Has me thinking,'Where's the catch' so use your common sense. With that in mind don't overspend on this bike - keep in perspective what it is and that will be less frustrating in the long run.