I was thinking about this a bit more.
The battery is good for a max of 40 miles (more or less).
Realistically, folks will only use the battery once per day (charge overnight, use for the first 40 miles of driving the next day).
The competition for this kind of car is a hybrid or similar car, getting 40-50 mpg.
So the battery saves you a max of ~0.8 - 1.0 gallons, compared to a hybrid or other high efficiency car.
Let’s say you can fully utilize that savings 6 days per week (long commute, plus some weekend driving.
That means you’re saving about (0.8-1.0) * 6 * 52 = 250 - 312 gallons of gas per year.
As long as gas is in the $2.75 ish range, that’s about $688 - $858 / year. But you do have to pay something for the electricity that charges the battery, reducing those savings somewhat. And this is under near ideal usage (lots of daily mileage).
For those who make the decision purely on economics (rather than novelty, green-appeal, or whatnot), and who set a payback time of 6-10 years or so, then this kind of Volt technology should probably command a premium in the $4-8K range (ish) relative to a good hybrid.
I haven’t done an apples-to-apples comparison against a similar hybrid, but I doubt the Volt will be in that sweet spot, price-wise, initially. Still, the novelty will carry it. The key question is if GM can get the price down and still earn a reasonable profit on it. I’m guessing they can, but that’s a rather wild, uninformed guess.