The batteries, however, have already been installed in nearly a dozen Wal-Mart stores as part of a test program.

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