Ahhh, you noticed. Many peolpe ask what the battery is for...
Yes, got me a motor from China, put a 36 V battery into a bottle, controller is hidden under the carrier. Some magnets on the small chainring and a sensor at the bottom bracket to activate the motor as soon as I am pedalling.
Three speeds selectable (switch at the top of the seat-tube).
Stealth-drive ;-)
Throttle at the handlebar is optional, but I did not want to run any cables along the frame.
Next project is an electrified Mountain Cycle San Andreas, but mwith the motor driving the cranks, to have full power in any gear.
But I still love to cycle the old-fashioned way, this is just the engineer in me wanting to experiment.