I just came across these energy harvesting batteries from FLEXEL which derive energy from the environment such as existing radio waves and vibrations. These are millimeter thick high density rechargeable batteries which have been created from thin films.

These are flexible batteries which can be molded into any shape and attached to RFID chips and microchips. Created from environmentally friendly materials the good thing about these batteries is that they can be recharged by pointing a cell phone to it.

This power packed battery delivers more energy per square cm as compared to any other rechargeable flexible thin film batteries available. It can be recharged at even low voltages which may not be a possibility in case of other normal batteries. It can be manufactured using cost effective printing process and hence are suited to power a range of ultra small electronics.