Chemistry determines the cell voltage (1.2V or 1.5V and there are others like Lithium at 3.0V), whether the battery is rechargeable, and how the voltage changes as the battery discharges i.e. at what voltage is the battery considered to be flat or fully charged. Switched mode power supplies. One more point.
The Average Bike Riding Speed. The average road bike speed is between 11 and 12 mph. Bike riding speeds vary widely depending on your riding conditions. When you are zooming down a paved hill, your speed may increase to over 20 mph, while you may slow to only a few miles per hour when you are climbing a steep or rocky grade.
The answer really depends on a lot of factors (e.g. bike type, terrain, rider fitness, & speed preference, etc.). I used to ride my 10 speed road bike in my neighborhood over a 3.3 mile course & the best I could do was ~22 mph (when I was much younger & in very athletic condition). I'd guess an average rider who rides for general exercise would probably ride at approximately half that speed (~11 mph) on the same type of bike.