IT’S FINISHED!!
I finally got the box working and it’s a dream. I can’t quite believe it’s done. I still have a few software kinks to iron out, and I may need to add some shielding between the signal wires and PCBs, but for the most part it’s working incredibly well. Charges to 100% in 2-3 hours, and I get around 3h of battery life.
Just bought a little action cam, so will be uploading videos of it in action very soon, including a walkthrough of how it works. In the meantime, here are the pics: