American companies are building batteries, hydrogen drones and homegrown fuel that could keep U.S. troops powered if a war cuts off foreign supply. Companies showed off their equipment at the Association of the U.S. Army’s annual meeting, which ended Oct. 14. Attacks on merchant ships around the Strait of Hormuz had hit their highest point since the Iran war began, Reuters reported Oct. 14, citing independent data. “The days of secure and predic…