I took my iPad Air 2 to the Apple Store a few days ago to get a battery replacement. Coconut Battery said it was 56%, but Apple's test said 81%, so a wide discrepancy. However, the tech said 81% was close enough, so it qualified for the replacement...
...but, they said they can't do it, because they can't order the replacement as it is unavailable. 😡
So, I went home and chatted with Apple directly, and they also said they can't do it via mail-in, because only the service shops can do it. 🙄
This device is now listed as vintage, but NOT as obsolete. In theory, vintage products still qualify for the battery replacement, but in reality, not so much.
BTW, the 81% Apple claims seems like bullcrap to me. And more importantly, the battery behaves very erratically. It will sometimes just randomly shut off when the power drops below 30%. And when you turn it back on, it says it's 10%... and then will shut back off at 7% or whatever.