Tesla is already building a 5-million-square-foot battery factory. It's not big enough. That was the message from Tesla Chief Executive Officer Elon Musk this week while discussing, for the first time, the early response to his new product line of storage batteries designed for use in homes and businesses. The numbers are impressive. In the first few days of reservations since the battery announcement on April 30, Tesla took orders worth roughly $800 million in potential revenue, according to figures compiled by Bloomberg Business. ...