The distinction between various electric powertrain technologies is becoming more blurred as performance improves. A fuel cell uses some kind of hydrocarbon fuel, with hydrogen favoured for transport applications but heavy oils possible for static applications (steam reformation used to break down into H2 and CO2). Lithium-Polymer batteries are the latest generation of energy storage device but are capable of extremely high rates of charge and discharge. Often the two technologies are combined to allow fuel cells to trickle charge LiPo batts in between demand peaks. For constant high power applications like helicopters this approach is of limited use, but LiPo will eventually give way to true high power to weight fuel cells. When will this happen? Eventually...