Okian Warrior writes: Billionaire Elon Musk will announce next week that Tesla will begin offering battery-based energy storage for residential and commercial customers. The batteries power up overnight when energy companies typically charge less for electricity, then are used during the day to power a home. In a pilot project, Tesla has already begun offering home batteries to SolarCity (SCTY) customers, a solar power company for which Musk serves as chairman. Currently 330 U.S. households are running on Tesla's batteries in California. The batteries start at about $13,000, though California's Pacific Gas and Electric Co. (PCG) offers customers a 50% rebate. The batteries are three-feet high by 2.5-feet wide, and need to be installed at least a foot and a half off the ground. They can be controlled with a Web app and a smartphone app.