Well they could just use the number of actual cells there are in a battery pack which I think is 7k. So that is 3.5 billion battery cells per year. I think 500k cars is much better to understand though.
Yeah, saying "3.5 billion battery cells per year [for cars]" could make it sound like they delusional expect every other person in the world to be buying a new electric car every year by 2020.
