The Shenzhen-based, Chinese automaker BYD Co's BYDDY all-electric vehicle sales soared by more than double in December, helping it outscore local rivals Xpeng Inc XPEV, Nio Inc NIO and Li Auto Inc LI combined for the full year as well. What Happened: BYD, which is backed by Warren Buffett-led Berkshire Hathaway Inc (NYSE: BRK-A ) (NYSE: BRK-B ), sold a record 48,317 battery-powered electric vehicles in December, a jump of 148% year-over-year and 4.7% over the previous month.