How about that bluetooth throttle? 
The throttle controls are connected by wires as Bluetooth testing was not successful. When the Bluetooth battery was low, the motor cannot receive any further signal until battery was replaced.
If the throttle device transmitted the bluetooth signal for a split second, but
only when the throttle position varied, it would greatly prolong the battery life. At a constant speed, no signal would need to be transmitted until the throttle is moved to another position.
The throttle could have a reed switch or similar which would disconnect the battery when the throttle was fully closed to ensure maximum battery life. A small capacitor would enable the throttle to send a last "no throttle" signal before it was fully discharged. Simply moving the throttle would automatically reactivate its position sensing circuitry.
This would work similar to a wireless cycle computer, which only sends one tiny pulse per wheel revolution instead of a continual signal.
Their batteries usually last for ages, unless you're unlucky enough to park your bike with the magnet right next to the reed switch.
A "low battery" signal could be sent to the controller, which would then beep regularly to indicate that the battery needs replacing.
(like smoke detectors)You could possibly switch over to a built in emergency battery or have a quick charge option using the hub's usb connection?
I'm sure GM could turn the prototype version into a completely viable product with a bit more thought and development.
Yao,
You should forward these comments to whoever deals with your design and development projects, and then post a video response.
I think I can guess the response already. 
Alan
