Battery replacement iPad Air 2

You can establish eligibility and cost of a battery replacement in your country/region here:

iPad Repair & Service - Apple Support

You might choose 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 - prior to committing to a battery replacement or other repair:

Genius Bar Reservation and Apple Support Options - Apple

For practical purposes, in lieu of replacing the battery and returning your own iPad, Apple usually exchange the iPad for a renewed/refurbished iPad of the same model and specification. The cost of the exchange is the same as would otherwise be charged for the battery replacement. The exchange device will have a limited warranty.

Be aware that Apple do not supply original OEM batteries outside of its own network of AASPs. As such, third-party repairers that offer battery replacement will not be using genuine components. Use of non-OEM batteries may result in loss of some functionality - such as the TouchID sensor being disabled.

The cost of replacing the battery in an iPad Air 2 can vary depending on where you get it done. Typically, it ranges from $99 to $129 if you go through Apple's official service, but prices can vary at third-party repair shops. It's always a good idea to shop around and compare prices to find the best deal.