Tesla's move into batteries has been long expected. Tesla CEO Elon Musk hinted back in February at the company's intentions to build batteries, and in March he tweeted that a "major new Tesla product line — not a car" was to be unveiled on April 30.

In an email to analysts and investors, also seen by BuzzFeed News, Tesla head of investor relations Jeffrey Evanson confirmed that the company planned to introduce the "Tesla home battery and a very large utility scale battery."

Evanson added: "We will explain the advantages of our solutions and why past battery options are not compelling."

Bloomberg has more detail on Tesla's intentions, revealing that the company is already actively testing out the batteries in a pilot program in California. Some 300 homes have been fitted with the home batteries, along with 11 Wal-Mart stores. Cargill is another company planning to use the batteries.