I've been toying with the thought of getting an antigravity battery. Problem is, sizing and cost, and no idea of longevity in a daily driven car. Harley people use them religiously with good results. I'm still considering relocating the stocker to the boot though.
Ha, an order of magnitude is a very sophisticated way of saying, I really don't know.
Any form of high energy density is not considered safe and batteries are no exception. Plus the number of energy conversions required, always a loss. Coal burning plant to steam to mechanical energy, rotating a generator for electrical energy, using electrical energy converted to chemical energy, chemical energy back to electrical energy, to finally use a motor to convert that back to mechanical energy. And with a battery, even a dead one, hauling all that extra weight around.
Sure making big deal about weight when BMW manages to reduce 67 pounds of a 5,000 pound vehicle. Or the Eco for this matter.
IC engines are only 10-18% efficient, has to be some kind of engine to get that up to 95%, would like to see more research on this issue. Heck of a lot less energy conversion steps, and when your tank runs empty, not carrying all that dead weight around like with a battery. And can restore your energy supply in a couple of minutes.