If it were anyone else, I would be a bit skeptical...
We are talking about the guy who owns the largest electric car company, is about to own the largest battery factory (employing many battery chemists and other specialists), and owns the most successful of the private space launch companies.
I think he is well aware of the tyranny of the rocket equation (as well as how it applies to aircraft as they burn their fuel), the limitations of a battery, and the differences between theoretical maximums and what you get in practice. More importantly he is advised by those who really are experts, and past success suggests that he does listen and understand.
Tripling battery density would make it viable on shorter flights, perhaps even cost effective. If anyone is in a position to make that happen, he is.