Why was this devastating? Well, Samsung shares dropped eight percent - or $580 million in total value - after the Tweet went out. Tesla has long used Panasonic cells in its electric vehicles (but the Panasonic partnership was not exclusive), and is partnering with the battery company on the upcoming Gigafactory. As you might suspect, the value of Panasonic shares went up about three percent after the Tweet.
S and X cells are also Panasonic— Elon Musk (@elonmusk) June 8, 2016
So, what prompted the rumors that Samsung would be making cells for Tesla EVs? Mostly, the stories that Tesla and Samsung are working together. The stories are true, it seems, but it appears that the cells are for Tesla's home energy business, according to Automotive News.