SHANGHAI (Reuters) - Chinese battery giant CATL is in talks to buy a controlling stake in electric vehicle maker Nio's power unit, which runs more than 3,000 battery swapping stations in China, four people with knowledge of the matter told Reuters.

CATL made the proposal after announcing a maximum 2.5 billion yuan ($342 million) investment in the unit, Nio Power, in March, said the sources, who asked not to be named because the talks are not yet public.

The sources did not say how much CATL was offering under the proposed deal. However, one of them said Nio Power had been valued at more than 10 billion yuan during a 2024 fundraising round.

CATL declined to comment on the proposal when contacted by Reuters.

Nio did not directly address questions about the possible deal but said it was promoting joint construction of battery swapping stations "with multiple investors, including CATL".

"Nio and CATL will deepen collaboration on capital and business and further consolidate the strategic partnership to jointly build the largest battery swapping network globally," Nio wrote in a response to a Reuters request for comment.

CATL is ramping up investments in battery swapping facilities as chairman Robin Zeng aims to reinvent his 25-year-old enterprise, pushing beyond battery manufacturing to become a green-energy provider.

The company, which aims to lead a trend it says will replace a third of gas stations in China, announced a partnership with state-owned oil company Sinopec last week to build 10,000 battery swap stations. At least 500 of them will be built this year.

Nio Power, one of Nio's core assets, provides charging and battery swapping services to Nio drivers and other EV brands including Tesla and BYD.

The unit's potential sale reflects the intensifying competition Nio faces in China's auto market.

In an effort to ease consumer concerns over EVs' limited range, Nio has built some 3,240 battery swapping stations, mostly in China, that allow customers to replace a depleted battery pack with a fully charged one in less than three minutes.

The investments, however, have been a drag on the company's profitability.

Nio has also been co-developing EVs that can swap batteries with other automakers' models.

($1 = 7.3086 Chinese yuan renminbi)