Tesla's Powerwall was a big success from the moment that Elon Musk launched it last year. In fact, the device is sold out until mid-2016, and may have already hit $1 billion in sales. It turns out there was a lot of pent-up demand -- if you have solar panels, the device's giant battery lets you run your house after dark, and if you don't, it provides a reliable, long-lasting backup. Even though the first-gen Powerwall only started shipping a few months ago, Musk admitted at a private function (in the video below) that "we are coming up with the version two of the Powerwall probably around July or August of this year."