Elon Musk has revealed that he had once approached Apple Inc Chief Executive Officer Tim Cook to see if Apple would want to Tesla but the tech honcho had refused to have a meeting with him.

Musk said he made the move "during the darkest days of the Model 3 program". The revelation came a day after reports said Apple would soon landmark a announcement regarding its own self driving car.

Musk said he had offered to sell Tesla to Apple for a tenth of its current value. "He refused to take the meeting", said Musk.

He made the revelation on Twitter while replying to a Twitter conversation chain after Reuters reported Apple was looking to produce a passenger vehicle by 2024.

The iPhone maker started work on the autonomous car project, known as Project Titan, in 2014. The Project, which was shelved temporarily, was brought back to life again in 2018.

Central to Apple's strategy is a new battery design that could "radically" reduce the cost of batteries and increase the vehicle's range, the report said, citing people who have seen the design of Apple's battery.

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During 2017 and 2018, Tesla struggled to ramp up high volume production of the Model 3 sedan, with Musk at the time informing investors the company was mired in "production hell" because of problems with automated production systems at its battery factory in Reno, Nevada.

However, Tesla overcame the problems and has since racked up a string of quarterly profits. The electric automaker became one of the most valuable companies to join the S&P 500 when it became part of the widely followed stock index on Monday.

Shares of Tesla, however, ended 6.5% lower in its S&P 500 debut, amid news of potential competition from Apple.

Apple's automotive efforts, known as Project Titan, have proceeded unevenly since 2014 when it first started to design its own vehicle from scratch.

Central to the company's strategy for auto production is a new battery design that could "radically" reduce the cost of batteries and increase the vehicle's range.

In the same Twitter chain, Musk said "monocell", which Apple plans to use in its design, "is electrochemically impossible as max voltage is ~100X too low" unless they are bonded together.

Apple declined to comment while Tesla did not immediately respond to a Reuters request for comment.