Hi there - this is Lynda from nano. The reason we quote 8 - 16 miles for the 4Ah battery is that we have tested it on the following basis. If you hardly put any effort in, just keeping the pedals moving so the pedal sensor will allow the motor to be operated, on relatively flat ground, depending on your weight etc etc you will get about 8 miles from one battery charge. The upper limit is entirely up to how much you use the battery/motor but people seem to like an upper and lower limit to work with.