Complete all challenges in a week
Complete all the challenges for a single given week to unlock the first of the seven challenges. Once you've got your loading screen, head to quadrant 8H and head to the top of the eastern most tower at the prison. Stand near the edge and your secret battle token will appear!

If you look at the loading screen you unlocked, you'll be able to see the battle token in the image. It's above the guard tower at the prison, it's just barely visible!