It was designed for iPads that are connected to power for prolonged periods of time, such as when the device is used in kiosks, point of sale systems or stored in charging carts.
This appreciated new feature was designed to help maintain battery health by monitoring iPad for use in these situations and, as required, reducing the maximum charge level.
This iPad-specific capability should not be confused with iOS 11.3’s battery health assessment for iPhone available through Settings → Battery → Battery Health (Beta).
Battery health assessment, shown in a video embedded above, basically tells you about the battery’s maximum and peak performance capacity.
Apple’s support document sheds more light on iPad charge management:
iPad is a portable device that is designed to be used all-day on a single battery charge.
iPad uses rechargeable lithium-ion batteries which are designed to be charged and then discharged over their lifespan. When they remain at full charge for prolonged periods of time, battery health can be affected.
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.”
I, for one, was totally oblivious to the fact that leaving my iPad at full charge for longer periods of time affects battery health. It’s nice that Apple saw fit to describe how the charge management feature works to help clear up any confusion.