Your iPad will automatically limit charging to ~80% is some circumstances to protect the battery - this often occurring when the ambient or device temperature is relatively high.
As described, the iPad’s thermal management is doing its job - in trying to protect your iPad, in particular the battery, from irreversible thermal damage. Quoting directly from Apple… If your iPhone, iPad, or iPod touch gets too hot or too cold - Apple Support
“If your device gets too warm
iOS and iPadOS devices have built-in protections to prevent overheating. If the interior temperature of your device exceeds the normal operating range, your device will protect its internal components by attempting to regulate its temperature. Here are some of the higher ambient-temperature conditions and activities to avoid, because they might cause your device to change performance and behavior:
- Avoid leaving your device in a car on a hot day.
- Avoid leaving your device in direct sunlight for an extended period of time.
- Avoid using certain features in hot conditions or direct sunlight for an extended period of time, such as GPS tracking or navigation in a car, playing a graphics-intensive game, or using augmented-reality apps.
If the interior temperature of your device exceeds the normal operating range, you might notice these changes:
- Charging, including wireless charging, slows or stops.
- The display dims or goes black.
- Cellular radios enter a low-power state. The signal might weaken during this time.
- The camera flash is temporarily disabled.
- Performance slows with graphics-intensive or augmented-reality apps or features.”
If your iPad is inside a fitted case, try removing the iPad from its case while charging - as this will improve cooling.
If your iPad is being charged in cool environment - and you still see thermal management and high temperature warnings - your iPad or its Power Adapter may have a fault that will require investigation. In such circumstances you would be best advised to visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad, Power Adapter and charging cable:
Genius Bar Reservation and Apple Support Options - Apple
