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.
That's a 7.3 mile uphill (gradual) ride....the big thing I worry about is wind direction. A biker on a bike that is on flat level ground, no wind, can expend about 1 hp of energy to go 5 miles an hour or so...as you start to get over 10 or 12 mph, though, you have to start dealing with wind resistance.