The P3P Lipo has smart circuits in it. That means that the chip regulates the charge continuously.
If you look at a smart charger, a regular Lipo RC charger. They have a screen that shows how much it is charging by, and it varies a lot as battery reacts to the charge and it sometimes pauses to balance cells as well. The DJI does this invisibly inside the battery. Regular Lipo chargers have 2 connections, one for balancing cells and one for power some even have a temperature probe to cut current if Lipo gets too warm. The DJI charger only plugs in the power, so it is a dumb charger but a smart Lipo.