Relativity starts your automobile

I have already mentioned this interesting work. But it is so funny as to deserve a further click from Nature [469:269]:

Cars are started using lead–acid batteries, which generate energy using electrochemical reactions between lead compounds and sulphuric acid. Rajeev Ahuja of Uppsala University in Sweden and his colleagues modelled the reactions and found that as electrons move at high speed around a lead nucleus, their energy levels change owing to relativity. The authors conclude that the change accounts for 1.7–1.8 volts of a standard 2.13-volt lead–acid cell.