I don't think the bottleneck for charging is in the batteries, it's in electricity as an energy vector. By its very nature, someone is either instantaneously dispatching it from somewhere, or it's already being generated and curtailed. I just don't see that being cheaper than even biofuels in the long run, because time arbitrage matters. Making fuel with overcapacity that is worth zero (or less!) probably scales better than trying to store it all in batteries, because holes and containers will always be cheaper and easier to expand.