In the future Tesla may lease its home batteries rather than sell them to customers. The large batteries are meant to be kept in your home and used to store energy so you can access it later on. Mark Ahn (wikipedia) wonders: Why would you want to do that? There are a few reasons. In a traditional power setup, electricity that is sent to your home is then cycled back to the grid when you don’t use it. With the batteries, that energy could be stored instead of thrown back. Even better, the batteries could be set up so that they gather power when the electricity is the least expensive, and then store it for use later on when things get more expensive. Over time that could save you some serious cash.
Besides the cost benefits, stored power has some use benefits as well. If for some reason your town was to lose power, either for just a few hours due to a storm, or for days due to a larger issue, you would be able to still have power in your home, at least for a little while.