Apple Inc. worked with Chinese automaker BYD Co. 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.

As reported by Bloomberg on Wednesday, Apple has worked closely with Chinese automaker BYD. Both companies reportedly reached an agreement around 2017 to build batteries using lithium iron phosphate cells (LFP). The technology would significantly increase the autonomy of the car and was also considered safer than typical electric vehicle batteries.

Before the Project Titan was scrapped, Apple reportedly worked with Chinese automaker BYD on custom batteries for Apple Car for years, but ultimately abandoned that partnership too.

Apple worked with a Chinese automaker for years to design a battery system for its now-canceled car project. That’s according to Bloomberg, which reports that Apple was collaborating with BYD Co., a Shenzhen-based car company,

Apple and BYD teamed up around 2017 to build a battery system using lithium iron phosphate cells, Bloomberg reported, signaling just how far the iPhone maker went in its efforts to produce a car.