Two factors influence the feasibility of a battery type:
- How many Wh / kg can the battery store?
- What is the Price per kWH
see the calculation at http://www.withouthotair.com/cA/page_261.shtml how the first factor influences the achievable range of an elecrical vehicle powered by a battery.
$240-$280 per kWH for a Tesla according to http://www.torquenews.com/2250/what-makes-tesla-s-batteries-so-great
400 Wh / kg
There have been several companies claiming that they are close to the 400 Wh / kg target
Envias 400 Wh / kg claim was used to convince automotive companies like GM but the claim was exaggerated