When high-end car enthusiasts and collectors gathered for the U.S.’s swankiest car show in Monterey, Calif., last week, there was an unusual addition to the typical lineup of classic coupes and trucks. On the outside, the vehicle, an electric-blue early 1990s-era Porsche 911 sports car, wouldn’t stand out in these surroundings—it was far from being the rarest or most expensive vehicle zipping down 17 Mile Drive that week. But look under engine cover at the back of the 911 and you would find something exceedingly incongruous: the batteries, power electronics, and electric motors of an electric vehicle where a gasoline motor should be.

The idea of converting gasoline-powered cars into electric vehicles (EVs) is nothing new. The modern EV movement, to a large extent, was born …