Zhang Youping, a Chinese retiree, purchased an all-electric, small sport-utility vehicle from BYD — China’s largest electric vehicle maker — at an auto show for around $20,000 last month. Her family has bought three gas-powered cars in the last decade, but she recently grew concerned about gas prices and decided to go electric “to save money.” A few months earlier, her son had also bought an E.V. It was a $10,000 hatchback from Leapmotor, another Chinese manufacturer. This year, a quarter of all new cars purchased in China will be…