Electricity may be the costliest way to heat a house. It may be the cheapest way to run a car. The direct cost of powering a car may be half to a third the cost of filling it with gasoline or diesel. In the case of the Mini E just introduced, a fill-up, so to speak, would run you around $3.50 and there's less pollution. Here's how it works:

First Drive: All-Electric Mini E

With a Mini E, the 5,088-cell lithium-ion battery pack takes you as much as 150 miles under ideal conditions: flat roads, warm weather, no use of headlamps, no air-conditioning, coasting to stops to allow maximum battery regeneration. Regeneration accounts for as much as 20% of the range, Mini techies say.

5,088 laptop batteries in the back seat
Eventually you have to recharge the Mini E. Each one comes with a 220-volt wallbox that draws 48 amps of power - 10.6 kilowatts - then steps the output power up to 360 volts and recharges a nearly empty Mini E in 2.5-3 hours. (You can also recharge, overnight, using 120 volts AC power.) Mini says the battery holds about 35 kilowatt hours of energy, meaning it can supply 35 kilowatts for an hour or 1 kilowatt for 35 hours. Your laptop may have 50 watt-hours of energy, but that's because you've got six lithium ion cells rather than the 5,088 computer-industry-standard 18650 3.7-volt Li-Ion batteries ($4-$6 apiece in thousand-lot quantities).

While resistance heating in homes is woefully inefficient, electric motors are amazingly efficient, at least twice as efficient as a combustion engine. A typical recharge of a nearly empty battery will be 29 kilowatt-hours worth of energy, says BMW Group engineer Unrich Kranz, and the average price of electricity in the U.S. is about 12 cents a kilowatt-hour. Ergo, $3.48 to travel another 125-150 miles. A Mini Cooper would use 3-4 gallons of premium gasoline to travel the same distance, and at $2.50 a gallon for premium (current nationwide average), that's $7.50 to $10. Worst case, living in New England with an average energy cost of 17 cents a kilowatt hour, the electric fill-up is about $5.

But: "Alternative energy will not be cheap"
That's only the direct cost. Taking everything into consideration, says BMW marketing executive Wolfgang Armbrecht, "Alternative energy will not be cheap." How not cheap? BMW won't disclose the cost to build a Mini E but allows as how the battery pack from AC Propulsion of Los Angeles runs 30,000-40,000 euros, or US $38,000-$51,000. And lithium ion cells in laptops are good for hundreds, not thousands of charge-discharge cycles. That won't be a problem with a vehicle only meant to be in the hands of 500 test drivers for a year, but could be an issue for longer terms of ownership. Hybrids with combustion engines get around that by only running batteries in the middle 60% of their charge range (never discharge below 20% full, never recharge above 80% full and the batteries are good for 10, 15, or more years) but it would be a big trade-off for an electric-only vehicle.

Benefits from charging at night
There's also an environmental benefit: Power plants emit less emissions producing the energy than a combustion engine would. And it would be even cleaner if the car is recharged at night when high-cost, high-emissions sources idle back (coal, oil powerplants) and more of the capacity comes from water power and nuclear since nuclear plants are most efficient running at the same level round-the-clock. That suggests part of the long-term energy solution involves offering cheaper rates in the dead of night so you'll recharge cars or run dishwashers at 2 a.m. not 7 p.m.

Cost to drive 12,000 miles: $334 of electricity
Still, the bottom line for someone leasing a Mini E for $850 a month is that their cost of gasoline is zero and if they run through two complete charge cycles a week -- 250 miles a week, 1,000 miles a month, about 12,000 miles a year (Iet's ignore the extra four weeks in the year to keep it simple) - they'd spend $334 on electricity.