Consistent metrics are important.
(Just found this, btw: http://www.greencarcongress.com/2009/07/aist-lithium-20090727.html — it's a recent paper; has it been covered in El Reg?)
There are two main types of car: single-power types (e.g. petrol only, diesel only, electric only, etc.), and the dual power / hybrid power type.
For single power-source vehicles, the most useful metric is:
"Total Range@[x] km / hr. on a full tank / charge".
* The cost of providing that energy represented by that tank or charge is also noted. (This gives a comparable metric across the different types of battery, be it a Li-Ion or "tank of petrol". Both are just a form of energy storage.)
* Another key point here is that two figures need to be quoted: one where [x] is the typical national *urban* speed limit (approx. 50 kph in the UK) and the second where [x] is the typical national *extra-urban* speed limit (approx. 100 kph in the UK). This mirrors the current practice of similar figures for urban and extra-urban usage, with a combined average figure also shown.
The upshot of which would be an idea of how far you could go before you need to replenish the energy store, and how much that replenishment would cost you. For salesmen who tend to do a lot of long-distance driving, the extra-urban figure is of most interest; for city runabouts, which aren't meant to be used for anything other than local travel, the urban figure would be more prominent.
This gives a single, consistent metric across all forms of motive power. A battery is just a tank for electricity; that you have to charge it rather than refill it is irrelevant. It's just an energy store, like petrol, diesel or LPG. That energy has to come from *somewhere*, and it will cost you money.
The sticking point will be "cost of replenishment". Depending on how your electricity is generated, this can vary wildly for electric vehicles from nation to nation. The French have lots of nuclear power stations; the Swiss tend to prefer hydroelectricity; we Brits have rather more fossil fuel supplying our grid. (The US' power generation pattern follows a similar one to the UK, mixing some token carbon-neutral generation with a heavy reliance on fossil fuels.)
This means each country will also need to publish an annual, average cost per kWh and similar figures for other energy sources. This would give manufacturers a standard by which to show how much their cars will generally cost you to run.
Thus, for a hypothetical electric-only FIAT 500 wrapped around a Li-Air battery stack (see link at top), you'd see something like:
1600 km. @ 50 kph. (Li-Air Cell, cost for full charge / cartridge swap £5.00)
You can read that as: "£5 for a full tank which gets you 1600 km. of travel if you're driving at roughly 30 miles per hour." (The FIAT 500 is a very small city runabout car, so you wouldn't want to put big batteries or motors in it. It has little enough boot space as it is!)
I suspect that electric cars will take off almost overnight in countries like France, where most electricity is already produced by nuclear fission. As nations start to move away from fossil-fuel power generation—a process which can take generations—we'll see petrol and diesel slowly becoming marginalised, until it's only found on a few specialised vehicles, such as some military, farm and construction machinery.
(I'm in favour of more fission plants here in the UK. They're not perfect, but they're better than burning coal, gas or oil, all of which can be put to far better, more constructive, uses. Fission is a stopgap, buying time for researchers to sort out a better replacement. Which might be fusion, or might turn out to be something else entirely. Such as an emphasis on micro-generation.)