Your iPad contains no user serviceable parts - battery or otherwise.
Be aware that Apple does not supply OEM components outside of its own network of Apple Authorised Service Providers (AASPs) - and as such, any battery that has been purchased from a third-party will not be an original part.
Many components, OEM batteries included, are serialised - and must be integrated using special software that is not available outside of Apple. If you change the battery yourself, some iPad functions (such as FaceID) will be disabled. Be aware that in replacing the battery outside of Apple's approved network, you will also forfeit all future hardware support for your your iPad; if the iPad were to be damaged or require further repair, you will be entirely on your own.
If your iPad requires a replacement battery, this is best entrusted to Apple or an AASP. You will benefit from both a new battery and a warranty.
iPad Repair & Service - Apple Support