As described, your iPad battery may have a fault, or may be reaching the end of its usable life. If the battery has failed or is failing, the iPad may unexpectedly turn-off - or may not successfully boot to a running state even when connected to its Power Adapter.
Are you able to use the iPad while remaining connected to your Power Adapter? If yes, while monitoring the indicated battery state, disconnect the Power Adapter; if the indicated battery state suddenly falls, or the iPad shuts-off, this test demonstrates the iPad battery having reached the end of its usable life:
iPad Repair & Service - Apple Support
Before committing to a repair, you might be best advised to seek assistance directly from Apple Support - and request a remote battery diagnostic test. You can contact the Support Team using the Support link at top-right or bottom-left of this page.
Alternatively, you can initiate and manage your support cases from Apple devices using the excellent Apple Support App. If not already installed, the App can be downloaded from the App Store:
https://apps.apple.com/app/apple-support/id1130498044
