When the maximum charge level is reduced to protect the battery, the power indicator in the iOS status bar will display the charge based on the adjusted maximum battery level.
The maximum charge level will revert back to the previous level when iPad is no longer connected to power for prolonged periods and “as conditions and battery health allow.”
The main battery news of the 11.3 update was the addition of the iPhone battery health feature. I haven’t seen the iPad charge management feature discussed much. With more people using their iPads as their only computers, the lesson here is not to keep your iPad plugged in all the time like you would with a desktop computer.