The world’s biggest handset vendors got together on Wednesday to launch a common energy rating system for mobile phone chargers, cluing consumers into the best, and worst performing models.

The five star rating system was developed and is supported by Nokia, Samsung, Motorola, LG and Sony Ericsson, under an industry wide initiative to reduce the environmental footprint of telecoms products.

Many consumers are unaware that phone chargers continue to use electricity when disconnected from the phone but left plugged into the wall socket. Device vendors claim about two thirds of the energy used by mobile devices is wasted in this way.

So the new rating system indicates how much energy the charger uses when left plugged in after charging is completed, with five stars for the most efficient chargers down to zero stars for the ones consuming the most energy.

The ratings are based on the European Commission’s energy standards for chargers and the internationally recognised Energy Star standards set by the Environmental Protection Agency in the US.

The device makers are also working on introducing visual alerts into their devices to remind people to unplug the charger from the mains when the battery is fully charged.