The choice of battery is ultinately detemined by the controller. So you could clarify this by telling us whether it is a bafang 750W mid motor, or if it is a 750W hub motor. The mid motors have the controller inside the motor. The hub motors use an external controller. So tell us which motor, and if it is a hubmotor, what is the amp rating of the controller.
The simple answer is you get a 48V 19Ah battery with ability to source 30 amps, but you could get by on less, depending on what motor you actually ordered. Or depending on what you ordered, you could get a 52 V battery for higher performance.