[crpatino]

Batteries are cheap to charge in-place. Once you load those into a train you have to add the cost (both economic and in energy conversion rates) of moving the whole mass around in a diesel powered vehicle.

We already do that with alkaline batteries, and we pay premium price per BTU because of the convenience of begin able to carry small quantities of electricity around. But if you want to move city-powering amounts of it (think millions of Megawatt-hour), I am guessing a grid is more efficient.