Sony showed a battery that is powered with sugar.

The Sony sugar battery generates power using glucose. Enzymes breaking up the sugar and besides electricity, water and carbohydrates are freed.
Currently a single cell offers 50mW. Sony demonstrated a sugar battery powering a Sony Walkman.
The size to output ratio is still not competitive with lithium ion batteries, but this is an interesting battery technology. My bet is on fuel cells though.
Via this Sony press-release (Japanese). Sony is not the first to make a sugar battery. We reported about Researchers at the Saint Louis University in Missouri inventing a sugar battery in March.