This does get into perspective from Apples point of view they want to sell you a new iPad when your current one dies.
From our perspective it is repairable but tricky! Review this IFIXIT teardown: [guide|30592|iPad Air 2 Teardown]. As you can see the battery can be removed and it does take some skill and the proper tools to do it.
As a reference here's what parts are available for the iPad Air: [http://qualityrepairparts.com/wholesale-ipad-parts/ipad-air-parts/|iPad Air Parts] as you can see someone does sell the battery so it can be replaced. While this is an iPad Air not an iPad Air 2, in time the parts for it will become available, it's just to soon for the Air 2 parts.