"Just use better batteries" does make it sound trivial, but those were not my words at all. Saying that we need to "vastly improve energy density" felt, to me, to be conceding that it would require vast effort. That is why I also offered an alternative - carbon-based fuels. They pack an extremely high energy density, but are volatile and would require very special approaches to make them safe and easy to refill. In other words, no matter which option one looks into, it will take a lot of work to improve on the state of the art. By no means did I intend to convey the message that I think otherwise.