Tesla had its best day in over 4 years after promises of a profitable second half

Shares of Tesla closed more than 16 percent up Thursday, a day after CEO Elon Musk and the automaker promised a profitable second half of 2018 during its second-quarter earnings report.

The stock had its best day since December 2013 when it gained 16.53 percent. It's a welcome stock bump for investors, who sent Tesla shares skidding more than 5 percent after the company's last earnings report in May and Musk's bizarre comments during the earnings call with analysts.

On Wednesday, Tesla posted a greater-than-expected loss per share for the second quarter and revenue that just edged out Wall Street estimates. Musk helped lift share prices with apologies for past bad behavior.

By the close on Thursday, shares of Tesla had gained 12 percent in 2018 and were just 11 percent off 52-week highs.

- CNBC's Ariel Shapiro contributed to this report.

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