How high can you fly?

Mark wrote:
I keep running across new technologies and it takes time
to come up with hard data and numbers that would allow
me or anyone else to tell you what the new batteries
weigh or what their energy density and durations are.

I'm trying to point out that some of us have some of idea of what is
possible within the next 10 years and what the ultimate physical limits are
of energy density.

Wikipedia has a table of energy densities for several battery technologies
compared with traditional energy storage:

http://en.wikipedia.org/wiki/Energy_density

So far as I can tell it appears roughly correct.

Avgas has an energy density of ~44MJ/kg.
The best _emerging_ battery technology has an energy density of ~3.6MJ/kg.

Ground vehicles can still be useful with low energy densities, but aircraft
rapidly decline in utility. Put another way, airlines will be flying jets
burning jet fuel for the forseeable future.