A big motivator is California’s air pollution control regulations, which require the six biggest automakers to derive 4 percent of sales from zero-emission cars this year. Nine other states, including New York and Oregon, have similar laws. By the 2018 model year, the ZEV requirement in all those states will jump to 15.4 percent and include smaller companies such as BMW. Daniel Sperling, an environmental engineering professor at the University of California at Davis and a member of the state’s Air Resources Board, defends the ZEV program as a way to promote technologies California needs to cut carbon emissions. Still, he expects the Air Resources Board to reduce credits for battery swaps. “We want to be generous in supporting these technologies, not obscene,” he says.