Tesla's reign as most valuable carmaker appears to have been short lived.

Shares in the electric car and new energy specialist have fallen this week despite news of Friday's Model 3 start of production and a non-auto deal to supply energy storage to South Australia state. This appears to have been offset by a poorer than expected showing in an insurance group crash test in the US and by lower Q2 sales, explained by the company as due to a shortage of battery packs. There have also been suggestions the upcoming, and much cheaper Model 3 may take sales from the ageing Model S which has been little changed since launch several years ago.

Reuters last night reported Tesla shares fell for the third straight day on Thursday.

Overall, the stock had fallen about 13% this week, taking almost US$8bn off the company's valuation.

That put General Motors back on the top perch with market capitalization of $52.71bn as Tesla dropped to about $51.8bn, the news agency said.

Reuters earlier reported mining giant Glencore would sell up to 20,000 tonnes of cobalt products to a Chinese company, a move that in turn helps Volkswagen secure car batteries for its shift to electric vehicles.

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