The report relied on data produced by the Department of Energy, the Environmental Protection Agency, the Argonne National Laboratory and from auto manufacturers. It considered emissions from oil extraction, refining and transportation to gas stations. On the other hand, making lithium-ion battery packs also produces a lot of pollution. UCS based its modeling on the Nissan Leaf and Tesla Model S -- the two best-selling electric cars in the . Each has a different greenhouse gas emissions profile. The bigger the battery, the more pollution results from its production. That's why the smaller Nissan -- which also has less than half the range of a Tesla -- offsets its excess manufacturing emissions in about 4,900 miles, or six months of driving. The Tesla offset comes within 19,000 miles, or 16 months of operation.