I, for one, can't wait to replace my battery! Why? Because in 5-8 years, new generation LiIon packs will be readily available for all hybrid models. From Wikipedia:

 

Assuming you get free electricity to charge the battery. I really hate this assumption. I am very pro-PHEV, but I think that the assumptions behind statements such as 500 mpg and the reported $0.75/gallon of gas equivalent are deceptive. The $0.75/gallon of gas equivalent assumes a comparison to a car that only gets 25 mpg (but at least it does take into account the cost of electricity at $0.03 /mile).

 

My TCH replaced a V8 hand-me-down that got 18-21mpg. 24 if I hypermiled it! And I don't think they're any more deceptive than the last 20 years of EPA MPG ratings but point definitely taken!

And yes, the cost of the battery upgrade would be way more than just paying for gas (generally). However, as the early adopters pay for emerging technology, the costs in production come down when the market adopts the technology (how many hybrid models are coming out in the next two years compared to the last two?). Eventually, in the long, long, long run, everybody benefits from the overall impact.

So, while I'd LOVE to own a Tesla, I'll settle for now!

 

I think that the way I look at the old EPA estimates is "you can get this if you really try." Now they are based on more real-world scenarios, such as hills and A/C usage. So the new estimates are "more than likely, you will get this MPG." I don't really think of either one as deceptive.

However, I do think it is deceptive to say you can get 500 mpg in a PHEV. Why not just say you can get 1,000,000,000 mpg. You can, the way they define it (eg free electricity).

Again, if you take into account the cost of electricity, and compare it to a prius that can't be plugged in for a milage comparison, then that would be honest. The calculations I did were based on 8.32 cents per KWH and 46.9 mpg for a non-plug prius. This equates to about 2.08 cents per mile, or $0.99 / gallon equivalent.