All the Prius cab drivers that I have talked to keep saying that the car has to run on the IC engine a lot as the electric motor hasn't got enough power for hills, heavy loads or speedy departures from intersections. They save a lot on fuel but I'm betting all that saving will go on the first set of replacement batteries and the old ones will go into a landfill that is filling even faster with eco-friendly car parts because they are too bloody expensive to fix when they are worn out.