A number of companies are trying to figure out ways to make cellulosic ethanol by breaking down sugar with microbes and enzymes. Sony has used similar principles to build a battery.
In short, the anode of the battery consists of enzymes--a protein that speeds up chemical reactions in living organisms--which digest sugar while the cathode that breaks down oxygen. The two are connected by a membrane. The anodie extracts electrons and hydrogen. The hydrogen migrates through a membrane to the cathode side and makes water with the oxygen. Those loose electrons go to power your MP3 player or phone.
Test batteries produced by Sony have managed to produce 50 milliwatts. The company even strung a bunch of them together to power an MP3 player. Sony presented a paper on it at the 234th American Chemical Society National Meeting & Exposition in Boston, one of the premier and longest running scientific conferences in the world. (Although there were far more leeching papers back in the 1770s.)
Biologically-inspired processes like this are increasingly a big deal in the research community. What are microbes, after all, but little chemical factories. They eat sewage and, though the wonders of the metabolic process, produce methane. Beer is essentially waste product from the digestion process of yeast-think about that the next time you buy a six pack.
With cellulosic ethanol, enzymes created by microscopic organisms break cellulose down into sugars and then convert the sugar into alcohol. The big challenge many companies are facing is that 1) breaking down cellulose isn't easy and 2) a lot of microbes die in high concentrations of alcohol.