Even with heat being wasted, the energy density is so high that it still outpaces batteries by a significant margin. For example... try making a battery powered 747 airliner... you can't because the weight is too high.
I'm surprised many people missed this. That 10% of 50MJ/kg is still more than 100% of 1.8MJ/kg (current advanced batteries) and substantially more than 100% of 0.18MJ/kg (lead acid). Which my comment was about manufacturing and technology over a hundred years ago. My comment was focused on the latter comparison and not the former (which was just a side note). I guess everyone latched onto my side comment.
