Proponents maintain that state-of-the-art battery energy storage systems are safe, but more localities are enacting moratoriums. At least a few dozen localities around the United States have moved to temporarily block development of big battery systems in recent years. A large battery system might consist of rows of shipping containers in a fenced lot, with the containers holding hundreds of thousands of cells. China and the United States lead the world in rapidly adding battery storage energy systems. New York has an ambitious goal to add 6,000 megawatts of energy storage by 2030, half of it large-scale systems.