Has anyone ever tried using a different battery (such as Tattu - 16000 mAh) on Matrice 100? I know it has been tried on M600 but don't know if it's doable on M100. Idea is to increase the flight time to 50+ minutes. Any pointers?

That is a third party type battery so we are unable to advise on that point. You also have to watch for the warranty implications of using such a product. If you are still considering using this battery, make sure you go to the Specs section of the Matrice 100 to make sure that the battery matches: https://www.dji.com/matrice100/info#specs