Termites manage to power themselves by eating wood, which is a pretty neat trick. Sony has just come up with a battery that does the same thing: feed it shredded paper or cardboard, and it produces enough electricity to run an MP3 player.
What Sony has come up with (actually, they've been refining it for years now) is a thin sheet of material called a "bio-battery." The basic design uses an enzyme to break down sugar and turn it into hydrogen ions and electrons, creating an electric current and water. Bio-batteries like these can run on all kinds of things, from soda to fruit juice, but the problem is that all of these sugary liquids are just so tasty, and given the choice, most people can't help just drinking their battery power and not powering their batteries with it.
Okay, so yeah, that's not the problem at all.
Still, it would be a lot more useful to power a battery with something that's not as tasty or useful as fruit juice, which is why Sony has added another enzyme into the mix that can break down cellulose into sugar. Cellulose is made of long chains of glucose (sugar), and it forms the cell walls of most green plants. Cardboard and paper are both made of cellulose, but breaking those glucose chains down into usable bits is tough to do. The human digestion can't do it, but termites can, and so can Sony's pet enzymes.
All it takes to power this bio-battery, then, is a bunch of chopped up cardboard immersed in a solution of water and different types of enzymes. The first enzyme breaks the cellulose in the cardboard into glucose, which the second enzyme then eats to produce electricity. It's basically a little digestive tract that eats used paper products and poops out electrons and water, without relying on any heavy metals or chemicals or anything. Sounds too good to be true, and it almost is: as a proof of concept this technology is undeniably impressive, but it's going to be a while before bio-batteries like these output enough power to be useful as much more than novelties.