Oil vs the age-old vaporwabattery (was Why awe imminently repl

> 1kg (refined) oil ~ 50MJ * 40% = 20MJ of useful energy
> 1kg (advanced) battery ~ 5MJ * 90% = 4.5MJ of useful energy
> Oil still wins, but by a factor of four, not ten

Wikipedia says that a lithium ion battery only has an energy density of 0.54MJ/kg.
http://en.wikipedia.org/wiki/Energy_density

You seem to be comparing existing $500 gasoline engines to non-existant (and what price?) batteries. The electric motor alone in a Tesla Roadster costs $20,000, by the way. The entire car would reasonably be priced at around $200,000 MSRP, given the manufacturing cost of $140,000.

Other price evidence from the real world:
http://en.wikipedia.org/wiki/AC_Propulsion_eBox

"AC Propulsion offers the [eBox] conversion for USD $55,000."

> both fail to mention efficiency

Machine efficiency does not exist in a vacuum, and water does not flow uphill. Both are driven by natural forces. If gasoline is cheap, why might we be reasonable in expecting gasoline engines to have already reached their peak possible efficiency? Modern internal-combustion automobiles are as inefficient as they are largely because gasoline is as cheap (currently and forseeably) as it is. If gasoline were to become more expensive, we might reasonably expect gasoline-powered automobiles to become even more efficient.

When your fuel is dense and cheap, why bother designing for efficiency?

> 1kg (advanced) battery ~ 5MJ * 90%

No commercial electric car in the world has ever achieved anywhere near a 90% wall-to-wheel efficiency. Tesla has reported the Roadster's charging efficiency alone as only 86%:
http://en.wikipedia.org/wiki/Tesla_Roadster#Energy_efficiency