My bike has a 200W motor and for my regular 12km trip to work it’s going fine, have yet to find out how far a full charge will take me. The longest run was 35 km and it still ran well, took about 0.5 kWhr to recharge it. Compared to petrol in cost terms, I’m using 0.25 l/100km!!!
I mounted the battery on its side so that I could attach my panniers to the carrier rack.