Tesla Motors will be working exclusively with Panasonic on batteries for its upcoming Model 3, says CEO Elon Musk

A day after Reuters reported that Samsung SDI was closing in on a battery supplier arrangement with Tesla, it appears to be over. A source with direct knowledge of the matter had told the news agency that Samsung SDI was moving forward in talks with Tesla on Model 3 batteries and Tesla’s energy storage systems.

On Wednesday, Musk tweeted that the company was “working exclusively with Panasonic for Model 3 cells.”

A Tesla spokeswoman responded to Reuters’ inquiries on Tuesday by email that “Tesla works with all leading battery manufacturers around the world, however we don’t comment on the details of the programs with specific suppliers.”

Shares in Samsung SDI tumbled 8 percent on Wednesday after surging 6.3 percent a day earlier. Shares in Panasonic gained as much as 6.3 percent on Wednesday after Musk’s comment. It closed up 3.5 percent.

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Last month, Panasonic said that it was ready to move forward on its investment in Tesla’s “gigafactory” in Nevada if required to meet demand for the Model 3. The Japanese electronics company has made plans to invest $1.6 billion for the factory in phases over the next few years.

In April, Musk said that “tremendous demand” was spurring Tesla to push production forward two years earlier than initially planned for. Suppliers have said that its new target of manufacturing 500,000 vehicles in 2018 will be quite difficult to achieve.

A Samsung SDI spokesman declined to comment to Reuters.