Of all the car problems of many years, it was a battery explosion in my Camry while starting the car that scared me the most. (Internal short due to a seperator manufacturing defect.) These extremly high energy storage densities will make that explosion look like a small firecracker, unless the engineering is unbelivably good. I am very glad that Toyota is taking the conservative path. Each Prius generation has been a great success due to a total commitment to doing it right, not fast.