It may not seem like your mobile phone charger is sucking up that much energy - it only takes a couple of hours to power up a handset after all. But if you leave it plugged in all the time it's still consuming energy.

Nokia has joined forces with LG, Motorola, Samsung and Sony Ericsson to not only reach an agreement among all companies to improve the efficiency of chargers, but also make it easier for consumers to see which ones use the least energy.

The new rating system shows how much energy each charger uses when left plugged after charging is completed. The ratings covers all chargers currently sold by the five companies, and range from five stars for the most efficient down to zero stars for the ones consuming the most energy.

Consumers will also be able to see the info on each company's website, so they can get the lowdown in advance.