Battery energy density is hard to improve. Lithium is already the smallest non-gas atom, and we're within an order of magnitude of its absolute limits. Even tho

Battery energy density is hard to improve. Lithium is already the smallest non-gas atom, and we're within an order of magnitude of its absolute limits. Even though it seems like batteries have improved a lot over the last two decades, the vast majority of that is due to electronics that consume less power, not increased battery capacity. That said, cost can still be reduced and cycle life can still be improved. And there are exotic ideas for better batteries too. [1] An article on the progress and limits of batteries: http://www.nature.com/news/the-rechargeable-revolution-a-better-battery-1.14815 http://www.nature.com/news/the-rechargeable-revolution-a-bet... (might be behind a paywall)