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.