iPad and iPhone are portable devices that are designed to be used all day on a single battery charge. There are times, however, when an iPad or iPhone is connected to power for prolonged periods of time, such as when it's used in kiosks, point of sale systems, or stored in charging carts. iPad and iPhone use 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.
iPad with iOS 11.3 or later and iPhone XS, iPhone XS Max, iPhone XR, or later with iOS 12 or later include a charge-management feature to help maintain battery health. This feature monitors these devices for use in these charging situations and, as required, reduces the maximum capacity of the battery. The battery indicator will display the charge percentage based on this adjusted maximum capacity. The maximum capacity will revert back to the nonadjusted level when iPad or iPhone is no longer connected to power for prolonged periods and as conditions and battery health allow.