It focuses on changing the way a device's digital memory works, as this   consumes much of the charge.

At the moment mobile phone memories contain thin metal wires. Every time   information is accessed, electricity is passed through them to retrieve the  data.

The electrical engineers thought that if the size of the components used to   store and retrieve the information could be reduced, so could the amount of   electricity.

They have discovered a way of using carbon nanotubes - tiny tubes 10,000 times   thinner than a human hair - instead.

Feng Xiong, a graduate student on the team who was lead author on a paper, to   be published in the journal Science, explained: "The energy   consumption is essentially scaled with the volume of the memory bit."By using nanoscale contacts, we are able to achieve much smaller power   consumption."Prof Eric Pop, who led the project, said: "I think anyone who is dealing with   a lot of chargers and plugging things in every night can relate to wanting a   cell phone or laptop whose batteries can last for weeks or months."He thought that the method could improve a mobile phone's efficiency so much   that they could be made to run simply by harvesting heat, kinetic energy or   solar energy.