“A little bit of slope makes up for a lot of y-intercept”
So, sure, right now, the energy density of gasoline makes terribly inefficient combustion engines practical. But their energy density isn't going up (while lithium batteries are improving and coming down in price), certainly gasoline isn't going to get cheaper, and as for the combustion engine, well thats pretty played out after 100 years of trying to improve it.
Lithium-Ion battery energy density has about doubled in the last 25 years: http://futurist.typepad.com/my_weblog/images/2008/03/11/batt.... Even if gas technology stops improving tomorrow, it'll take 100-200 years to catch up on the energy density front.
From my armchair perspective, the Tesla Model S would be equally useful to any gasoline car for all but a handful of edge use cases, with only the minor change of adding a metal-air battery as a range extender for excessively long trips. And that's today, not 100 years from now.
The saying also deserves an addendum: "... if you've got the time."
The strength of the battery+motor electric drivetrain is that it's modular. Come up with another energy storage method, build it into a power pack, then plug it right into existing Tesla S cars, get the over the air software update, and you're back in business. There's also all of that frunk space.
Energy density is what I meant. I found some graphs to look at. You are probably right about there being lots more room for improving energy density.
Can you elaborate on your reasoning?
Frankly, energy density is a bit of an distraction. If we go by energy density alone, we would presumably all be cruising on Uranium, which energy density is... well off the charts.
But there a plenty of good reasons we don't fuel transport with Uranium, and there are just as many good reasons why we shouldn't continue to use gasoline.