I have an original iPad Pro 12.9’s. I guess that makes it 3 years old, ish. It’s battery had gotten very tired and I was finding it frustrating because I had to charge it throughout the day.
I live in New Zealand, and there’s no Apple Store here, but a couple of weeks ago I was in Sydney and I managed to get a drop-in appointment there.
The “genius” ran a diagnostic test, the battery was at about 75% capacity, so they happily replaced it - the entire iPad, that is, because the battery isn’t actually replaceable - for $150NZ ish.
So, I now have a brand new (original model) iPad, with about 1/3rd more battery life in it, and no scratches on the screen.
You can’t check your iPad battery life, but you can call apple support and they will run a diagnostic for you over the phone.
Worth checking out.