Surprisingly, this is one of the most common questions. While it is possible with systems with regenerative breaking, it would be very hard to pedal to produce enough power to charge the battery. It is much more efficient and cost effective to plug your bike in and charge it than to use pedal power. 20c of electricity would be about $20 worth of food if you were to pedal! Pedaling reduces the load on the battery, so any pedaling you do will make you go further and faster!