If you are not sure than you should do some more reading/research about what you can buy within your budget before buying. The only difference between the voltage rating on the throttle is for the battery indicator LEDs. If you take the 36V version and later upgrade to a 48V system, the LEDs that indicate the battery level (full, half and empty)won't work right. The throttle itself will still work fine and be able to control the motor speed.