http://www.dailykos.com/story/2011/0...=sidebyuserrec

You can't buy a lithium-air battery (yet). You've probably never even heard of one. They were only invented 15 years ago, and for now, they're still just laboratory curiosities.
But with the latest lab breakthrough, the lithium-air battery (also known as the lithium-oxygen battery) is nosing up into the energy density region seen in gasoline. If you're thinking battery-powered car, maybe your sights are too low. How does battery-powered airplane sound?


Since lithium is the lightest metal (in weight), any battery using lithium will be light. But since lithium-air batteries also have a light cathode, they are the lightest batteries known.
What's New

Now researchers at MIT have added carbon nanotubes to the cathode, with spectacular results. With a lot more surface area, the cathode can now hold a lot more lithium oxide, which means that the battery can run a lot longer before it needs recharging. The result is four times the energy density of the previous Li-air record holder: the old record of about 600 Watt-hours per kilogram has been upped to about 2500 Wh/kg, in the fully discharged state. This is getting close to the theoretical maximum is 3215 Wh/kg for a discharged lithium-air battery.

Rest: follow the linky.
Might give portable radio a new life ;)