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The new ratings system ranges from five stars for the most efficient chargers down to zero stars for the ones consuming the most energy.

If left plugged into the socket, chargers continue to use electricity even if the phone is disconnected. Nokia claims around two-thirds of the electricity used by mobile phones is wasted this way.

"If the three billion people owning mobile devices today switched to a four or five-star charger, this could save the same amount of energy each year as produced by two medium sized power plants," claims Nokia.

The scheme covers all chargers sold by Nokia, Samsung, Sony Ericsson, Motorola and LG Electronics.

The makers of the charges claim the scheme could also benefit them in the long run:
"This should be positive for us," says Markku Hangasjarvi, chief executive of Salcomp, one of the world's top four charger makers. "Such chargers are more difficult to produce, their average selling price is higher and they demand special know-how."