A:Answer Most likely it is on the lowest pedal assist level. Since the bike is 36v 10ah, that means it has 360 watt hours. An average ebike rider uses about 15 watts hours per mile with pedal assist at 3-5 (or since this bike only has 3 steps, 2-3). 360/15 = 24 miles using the 2 or 3 setting (which is 70% to 100%). Setting it to 1 would only use 20%, so you would use less watt hours per mile and that seems to be the circumstance where you can get up to 32 miles (using about 11.25 watt hours per mile). For more information on how this works, see https://www.youtube.com/watch?v=tluh8a9fTnQ.
I don't believe an additional battery can be purchased since everything is integrated into the frame.