Go to Settings > Battery > Battery Health to check the iPad battery health. If your iPad doesn't have that option, ...

Open one of your iPad’s analytics files (these files start with “Analytics” followed by a date). In the analytics file, tap ...

To check your iPad's battery health, you'll need to install a third-party app, which will require you to connect the iPad to a computer.

It seems to happen with all devices: you notice you don't get as much charge as you used to, and your iPad starts dying at inopportune times. Maybe it powers off when you still have 20% left, or just ...