FWIW the last time I checked, charging my 48V 13.5AH battery costs around a nickel according to my KillAWatt meter. I seldom run mine very flat. I try to keep it between 80% and 20% per the experts instructions. I charge to 80% and then ride it to work and home using maybe a quarter of the 60% available charge. If it is a hot day here in hot, hilly and humid central I might ask the battery for more boost so I arrive at work sweat free. On the way home I play a game to see how little boost I can get by with because at home I can shower. Can I do it on less than 2 Volts? Less than 1 volt? Usually I consume about 2 volts each way in moderate weather. Don't have a WH meter though I know I could calculate it. The trip in to work is easier than the trip home due to elevation changes.