Controllers from different batches of the same model can vary.
If you are buying BK5 BK8 BK8S how to distinguish between old and new models:
If your display and throttle are integrated and on the right side of the handlebar, your ebike is an older model and you will need to purchase an older model controller.
If your display is separate and on the left side of the handlebar, your ebike is newer and you will need to purchase a newer controller.
If you are not sure what kind of controller you need to buy, please be sure to contact us(email@example.com) and provide the order invoice from your previous ebike purchase and photos of the controller.