It will never be cheaper to put more batteries in a car. The smaller battery will always be cheaper than the larger one. So fine, we go 15+ years down the line, and a similar step up in battery to what we have now only costs 2500 dollars (inflation adjusted to 2014 dollars, assuming near-10% battery improvement per year). That's still a lot of money for something most people will use twice a year. And that's 15 years away. And there are Superchargers everywhere by then. And development costs to building such a niche car. Etc etc etc. It's a heck of a lot more significant and costly than putting a huge gas tank in a car, and notice that cars don't have huge gas tanks, there isn't an arms race for which car has the largest gas tank, even though it would be very easy for manufacturers to do this. There is a natural equilibrium and few vehicles stray outside of it.
And every public statement I've heard from any manufacturer suggests that batteries won't keep getting bigger forever. That includes Elon and JB. DaveT's link above seems more like a transcription error than anything to me (it's a summary from a forum member, not audio or even a transcript) and I would want to hear it for myself because I heard JB say the opposite about a month before that (he said he could only ever see cars hitting the 300-400 range maximum at the Cleantech investor's conference in feb 2013, and that is what I'm basing the things I've been saying on), and why I've been saying I could see them migrating a larger X or future "truck" battery to the S at some point in a super-sport style configuration but not continual increases in range. It won't be "like Apple" where they just double the storage in the battery every few years continually. The world is getting more data, but the world is not getting larger. In fact, the world is getting smaller. Continually increasing ranges make no sense. The focus will be fast charging.
And, as an EV advocate and person with lungs which like to breathe air who wants to get electric cars on the road NOW instead of 20 years from now, I believe talk of continually increasing ranges is dangerous, and all it does is satisfy the luddites who think the technology is not mature. It is, and it has been for some time. Tiny edge cases are irrelevant, as every product has an edge case, and the focus even we put on these edge cases seems counterproductive. Tesla will continue to work on expanding the car to be suitable for more people, but they will do so primarily through quick charging and there will be some people the car is not suitable for and that's totally fine. We are Osborning ourself every time we talk about 500 mile ranges which will never happen. But that's not why I think range won't continually increase (many of the reasons for that prediction are listed above), it's just why I say it a lot.
