USB charging
Hi what are you charging? It'll take more energy to charge than you get to keep and that has to come from somewhere, your pedaling effort or motor. Have you thought of a solar charger eg freeloader where solar panels charge an internal pack that you can then use to charge your device at your leisure. I've even seen a mini hand held wind turbine, but then thats extra drag tho minimal I guess. See firebox.com or simlar