We are trying to show the rest of the non-Drone public that we don't take pictures with weapons, We are also trying to tell the Public that despite their concerns we are actually a group of professionals doing a job, not just a bunch of Kids...
I don't think DJI has ever carried them (they'd rather you pay for something new). But if you google "dji mavic 2 controller battery" you should find links to sellers on ebay and other places, and you'll also get hits for "how to replace" videos...