NewScientist has a piece about a new battery technology developed recently in Singapore that uses urine to provide electric current. Only a drop or two is needed, but the urine powered battery could actually power your cell phone in a pinch:
The battery is currently suited for use with disposable devices – it is not yet ready to power laptops or iPods. "But if, for example, we place a small cellular phone or transmitter on a plastic card, the chip will work as a disposable biofluid-activated means of communication in an emergency,”
Until these batteries hit the market we suggest buying a Cellboost.
[via Textually]