On average, you need 6 to 15WH per mile depending on how hard you pedal. For 400 miles, that's 2400-6000WH, with the current Lithium batteries, the cheapest solution is to use 540WH, each weighs 3kgs with NCR 2900maH, costing about £350 each. So, 5 batteries at 3kgs each, 15kgs total. The bike...