J.C. Penney Co. Inc. recently was able to cut the power bills of six of its Southern California stores. The secret: batteries. Penney’s lithium-ion batteries, made by Panasonic Corp., charge by night in metal cases in the storage areas of each facility. Then, by day, when power from the grid costs more, they help run the stores’ air-conditioning. The batteries also help the stores avoid high utility fees, called demand charges.