Tesla has long boasted that its Model S sedan can go 265 miles (425 km) on a single charge, but the company's chief executive Elon Musk said it is 'only getting better'.

'It won't be long' before the Model S can travel 400 miles (645 km) on a single charge, Musk said in a tweet last week.

Musk announced his ambitious plans for an even larger battery pack several months ago as Tesla committed to upgrading its electric cars' batteries to support supercharger stations.

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Tesla has long boasted that its Model S sedan can go 265 miles (425 km) on a single charge, but the company's chief executive Elon Musk said it is 'only getting better'. Pictured is a Model S in Manhattan last May

His Tesla Energy division aims to add more battery technology and charging stations to accelerate the shift away from gasoline and make electric cars widely available and affordable.

Musk already leads the world's largest electric vehicle maker, and that history has already prompted skepticism from critics of the concept.

But Tesla has made only three vehicles a year for more than a decade, and its stock has quadrupled in the past 12 months.

The company now has about 360 stores and is building a factory in China to add another 400.

That is already rivaling sales of competitors, and its goal of delivering its first 750,000 vehicles in 2021, is inching closer to SpaceX, the aerospace and energy company where Musk also serves as chief executive.

Musk's Tesla Energy division aims to add more battery technology and charging stations to accelerate the shift away from gasoline and make electric cars widely available and affordable. Pictured is a Tesla Semi truck in the works

Tesla also has said it plans to introduce a smaller battery in 2020 with a range of about 215 miles (346 km), rising to around 500 miles (805 km) by 2022.

Tesla is currently using the same battery that powers the company's Model X SUV.

Tesla briefly surpassed General Motors Co as the nation's No. 1 automaker by sales in 2018 after shifting 468,871 vehicles last year, according to Autodata Corp.

But it lags GM in terms of overall sales by years and still is not profitable.