Nio has been offering the battery swapping service for free at least four times per month to existing owners. It is among only a handful of EV makers betting on battery swapping as a way to power electric cars.

Rival Tesla dismissed battery swapping as “riddled with problems and not suitable for widescale use.”

Nio said in February it would accelerate the expansion of its battery swapping network with a plan to build 1,000 swapping stations in China this year to bring the total number of such sites to 2,300 by year-end.

The money-losing company’s investments in battery swapping stations, however, have been questioned by investors for dragging on its profitability. Its net loss reached 4.7 billion yuan in the first quarter, compared to 1.8 billion yuan in the same period a year earlier.

Sales of Nio slid in April and May as the price war in China intensified and overall demand weakened. With its pure electric cars priced above 300,000 yuan, Nio delivered 43,854 vehicles in the first five months.

In comparison, Tesla’s China sales were more than five times Nio’s over the same period, while BYD sold 923,343 cars, thanks to its offerings of both full-electric and plug-in hybrids for less than 300,000 yuan.