I have several Bafang HD1000 48v builds I just received a new motor kit marked 52v and was told the controller C571-30-521 is compatible with both 48v and 52v. I researched it and found this statement online from another dealer: If you use 48V (max output voltage 54.6V ) battery for 52V controller C571-30-506. LCD will display wrong battery capacity. Battery cannot Completely discharged。 But motor work normal. The controller number of the previous 48v builds was C769-51-501. If anyone has more info on this I like to know, maybe there is an upgrade controller number out there that works with the HD1000 48v 30amp motor.