Api
Polestar 2 battery state API
Update in 2024:
It appears that Polestar is working on a proper API and folks have been figuring out how to get to the data used by the mobile app. See here for an example of a custom Home Assistant integration that surfaces quite a bit more than just the state of charge. This code will still work even with the existence of a polestar API but be aware that an official API might at some point appear.