hydrogen is a BEV the difference is the Battery is a fuel cell, and the major difference is that it take 10 to 15 minutes max to fill back to brim, which means all the oil companies want this as it means you filling up still. all a fuel cell is is a form of a battery, it takes charged water (simple terms) and puts it into the fuel cell, the fuel cell is the charged, when its low, you just re top up with charged water. and yes the by product out the rear is pure h2o… they all want the hydrogen route as its still a way to make money for all, its just very very pricey at the moment to develop.