Shares of Tesla Inc. /zigman2/quotes/203558040/composite TSLA +1.05% rallied 2.1% in premarket trading Monday, to buck the selloff in the broader stock market, as investors gear up for the much-anticipated Battery Day and amid troubles as fellow electric vehicle maker Nikola Corp. /zigman2/quotes/208704275/composite NKLA +2.30% . The stock's gains reverses an earlier decline of as much as 2.1%. The bounces comes as Nikola's stock plunges 26.6% ahead of the open, after the company said Founder Trevor Milton stepped down as chairman, in the aftermath of reports of investigations by U.S. regulators . Tesla's Battery Day is scheduled for Tuesday, with many expecting the unveiling of batteries with ramped up capacity and lower costs. Tesla's stock had gained 4.4% on Friday, and has run up 33.9% since Sept. 8, after falling 33.7% from Aug. 31 through Sept. 8. Monday's early rally comes as futures /zigman2/quotes/209948968/delayed ES00 -0.60% for the S&P 500 /zigman2/quotes/210599714/realtime SPX -0.30% drop 1.9%.