Maybe the app could change parameters like max voltage of a charge. From say 4.2v per cell to say 4.3v. That would be all it could do. And even though you would get more life out of battery. The risk of sparking and lighting up the battery would be increased dramatically. The longevity would be severely shortened. Etc
The app developers if they did that would be liable perhaps fr the danger caused so I doubt it. Let alone I believe DJI bake those settings into the firmware for the battery not impossible to change but unlikely.
Your instinct is spot on. Absolute scam. Unless it orders a new battery and has it delivered to your door.
They cannot throw lithium atoms into the battery and dji have the battery parameters optimised for factors to balance, speed of charge, amount of charge available, performance , safety and longevity. (Maybe longevity is the lower priority for them but it still would be a factor).