Dippin' in a Tesla is an expensive proposition, as we're sure you're well aware, but the US Department of Energy seems certain the cost of electric vehicles -- or at least their all-important rechargeable batteries -- will come down to reasonable levels. The government estimates a stack of cells good for 100 miles will drop to $10,000 by the end of 2015, and that 40-mile batteries for PHEVs will sink to $4,000 in the same timeframe -- both
