There is no Moore’s law for battery storage—the power of batteries doesn’t magically double every two years. And yet a funny thing has happened over the past six years. Rather than huge leaps and bounds, there has been slow, incremental improvement in the ability to manufacture lithium-ion batteries that can pack more power in the same space. Companies are doing a better job bargaining for supplies, rationalizing manufacturing processes, improving the chemistry, and generally doing the sorts of things that good engineers do. And so the performance of lithium-ion batteries has been improving by 5 or 8 or 10 percent each year. Because of the pace of incremental change, and because product cycles of cars are slower than they are for cellphones, an innovation revolution in electric cars has always felt distant. And yet we’re now finally seeing the beginnings of one.