Tesla Inc.'s director of battery technology has left the company, the latest in a raft of management departures from the automaker introducing its new Model 3 electric car. Kurt Kelty, who joined Tesla in 2006, was one of the longest-serving executives at the automaker led by Chief Executive Officer Elon Musk. He previously worked more than 14 years at Panasonic Corp., Tesla's partner on the battery gigafactory near Reno, Nevada. Kelty led negotiations with Panasonic on that plant, according to his LinkedIn profile.