Despite it making a third of the world's mobile phone batteries, until recently few people outside of China had heard of BYD.But the company exploded into the international consciousness late last year by beating Toyota and General Motors to launch the world's first mass-produced plug-in hybrid.There are also many questions about the environmental benefits of electric cars, given China's reliance on coal.Electric vehicles drive down carbon emissions best if they are charged at night with wind or other forms of renewable energy, but this is not currently possible in the country.But they do use energy more efficiently than both petrol-and diesel-driven cars,and environmental groups say electric vehicles can at least reduce the huge negative impact from the spread of car culture in China."Electric cars would be a big step forward," said Greenpeace executive director Gerd Leipold on a recent visit to Beijing."Hybrid cars have a better reputation than their ecological performance merits."