Can Apple replace the battery on an a pad air 2

Apple battery service usually means your wipe your iPad and send it in. For a flat fee of US$99 plus shippping, Apple sends you a refurbished iPad of the same model and specs fitted with a new battery. Otherwise you would have to wait a long time for the service.

This Apple support article covers battery service:

iPad Repair - Official Apple Support

Apple describes a refurb iPad as having a new battery and case, plus testing for proper function.

If Apple diagnoses your iPad and determines that your internal battery is failing or has failed, Apple does NOT do any type of repairs on iPads.

In lieu of actual $99 battery replacement, Apple will simply give you a replacement device, instead for the $99 battery replacement fee.

Best of Luck to You!