Apple worked with Chinese automaker BYD for years as part of its now-canceled car project, developing long-range batteries that helped lay the groundwork for technology used today, according to people familiar with the situation.

Apple and the Shenzhen-based company teamed up around 2017 to build a battery system using lithium iron phosphate cells, said the people, who asked not to be identified because the effort hasn’t been disclosed. The technology was designed to be longer-range and safer than typical electric-vehicle batteries at the time.

Though Apple doesn’t own any of the technology used in BYD’s current Blade batteries, the partnership shows just how far the iPhone maker went in its efforts to produce a car. The tech titan spent roughly $1 billion a year over the past decade on the vehicle project — often seen as one of the company’s "next big things” — before scrapping it in February.