Investors in Elon Musk 's car company, Tesla, have called on Musk to work at least 40 hours a week at the company.

The Tesla boss said he was back to working "24/7" and that he needed to focus on his companies, including Tesla. The stock is up sharply since April lows.

In a letter, some skeptical backers of the EV company have also asked its board to add a “new, truly independent” member and lay out a succession plan.