Toyota’s Prius is America’s best-known hybrid. Its 1,800cc gasoline engine is about twice the displacement of common bike engines, and its plug-in version’s 8.8 kWh lithium-ion battery weighs 265 pounds while the car weighs 3,365 pounds. Suppose we proportion a notional motorcycle hybrid battery to engine displacement. A battery half the weight of that used in a Prius would be like carrying an extra passenger on your bike, and it leaves out the weight of the power supply, electric traction motor, and associated details. Okay, let’s instead size the battery in proportion to vehicle weight plus one operator. Our 425-pound motorcycle and 175-pound rider total 600 pounds, while Prius plus driver equals 3,365 + 175 = 3,540 pounds or roughly six times as much. That might imply a much lighter battery of 265/6 = 44 pounds, plus more for motor and power supply, likely a total of at least 100 pounds. Still a lot of extra weight. And cost.