Here are the new fighting words: “miles per gallon,” generally known by its acronym, “mpg.” Why? Because when your primary motivation is provided by batteries and electric motors, you can gain some serious bragging rights. It's all kind of silly, since EVs hardly use gas at all, and therefore "mpg" is a seriously imprecise rating, but as GM pointed out to me, that's the measure people know.

GM fired the first shot by claiming its forthcoming (in late 2010) Chevy Volt “range extender” will get the equivalent of 230 mpg. That missile hit home, because soon everybody was buzzing about the Volt, and it got far more attention than it ever had before. Who knew Americans even cared about fuel economy? These are consumers who scarfed up copies of Car and Driver and Road and Track, neither of which ever met a horsepower increase it didn’t like. Until recently, auto “specs” didn’t even include fuel economy.

Not to be topped, Nissan shot back that GM should get over itself: The new Leaf battery car, it said, is 60 percent better than the Volt, getting a whopping 367 mpg. These calculations were made possible by a numbingly complicated mathematical formula put together by the EPA (which doesn’t involve actually driving the car; EPA testing of the Volt will occur early next year).

GM told me that it combined the EPA methodology with some real-world driver testing it did back in 2001. It turns out that most Americans don’t, on average, drive all that far in their daily commutes. The Volt performs best if it can cover most of its mileage in battery mode, and long trips mean using much more gas.

Earlier this week I spent some quality time with the MINI E, the very limited-edition battery version of the popular British car (actually made by BMW, but it still has a Union Jack on the roof as far as I’m concerned). The two-seater MINI E has some serious torque: It’s actually possible to chirp the tires from 40 mph. Its great fun to throw around on New Jersey byways around BMW headquarters.

Here's my first look at the MINI E in New Jersey:

The Mini E has 100-mile range (maybe 70 in the real world) and an AC Propulsion drivetrain. It had 85 miles of range on the tachometer-like gauge when I picked it up, and 55 when I turned it in. The 500 people testing this car in a global trial got 220-volt garage chargers, but it is also possible to…very slowly….charge it from an included 110 plug.

My point about the MINI E is that it actually has a window sticker, which somewhat clarifies the whole mileage thing. As Paul Weissler points out in a technical but interesting story on the Society of Automotive Engineers website, window sticker mileage and Corporate Average Fuel Economy (CAFE) mileage are not the same thing, and most window stickers will come in around 100 mpg. And that’s what the MINI’s says: 102 mpg city/94 highway. Not as impressive as “367 mpg,” but pretty good nonetheless.