Ipad 12.9 battery
How much does a replacement battery for an iPad Pro 12.9, first generation cost?
iPad Pro, iPadOS 14
We are all other users here and do not work for Apple; but, I believe that batteries are not being replaced by Apple (but best check with Apple support). Here is what I could find:
https://support.apple.com/ipad/repair/service
Use the get support link in the upper right corner of this page.