How plug-in hybrids, under fire for emissions, can regain their luster

Full-electric vehicles are the darlings of the automotive world. Elon Musk's Tesla enjoys a market capitalization that is the envy of conventional competitors, while investors are throwing billions in cash at unproven startups, hoping to catch a little of the EV magic. Automakers and governments are racing to declare ever-earlier end dates for the internal combustion engine.