Forget about rechargeable batteries that are plugged to a nearby electrical outlet - there are now Pee Powered batteries that are being tested in Japan. Dubbed the NoPoPo (Non-Pollution Power) Aqua Batteries, these will come in AA and AAA form factors. They are environmentally friendly and do not contain mercury or other harmful materials.

Japanese company Aqua Power manufactures batteries in various sizes that are using liquids as a catalyst causing a reaction between aluminum and magnesium resulting in a reload of the battery. Various liquids, such as water, coke, beer and even urine can be used.
The Non Pollution Power batteries are brand named NoPoPo, as the batteries are eco-friendly, not using lead, cadmium or any other fossil combustible.

Unfortunately, the NoPoPo batteries are on sale only in Japan at the moment and a European or US release date or price has not yet been mentioned. It’s rumored the batteries retain their charge for up to 10 years, but they can be recharged only a limited number of times. It’s also thought they could be slightly less harmful for the environment than existing battery compounds, because they can run off more, ahem, natural substances.

The batteries can be recharged with a variety of liquids, inserted into the chamber via a pipette and the basic principle is that a mixture of magnesium and carbon reacts when mixed with a liquid to produce, in the case of the AA battery, up to 500 milliamp-hours (mAh) of life. This puts them on a par with existing zinc-carbon AA batteries; however, existing alkaline batteries have a longer life of between 1700 and 3000 mAh.