From,
http://www.reuters.com/article/scienceNews/idUSSP22885120070824
Quote
Sony has developed an environmentally-friendly prototype battery that runs on sugars and that can generate enough electricity to power a music player and a pair of speakers, the Japanese company said.
It says that the power is 50mW but doesn't say anything about energy density. Still its a very good news.
Those who know the stuff should be able to tell how much sugar do I need per day to run my laptop? ;)