Then you're lucky. I had iPad 2 and Air 1. Older one is completely dead for 5 years now and doesn't react to plugged cable at all, while newer charges whole day and keeps battery for 4-5 hours.
Air 3 I've got on ebay-like site holds pretty well but the same model that my partner got from official dealer had always issues with touch recognition.
I keep mine unplugged and it gets surprising good battery life, and I think it kinda improved with the downgrade. On normal use I would get like 8-10 hrs screen on time. No spicy pillow yet, though I did have that issue with my old iPod.
No idea honestly, but the main reason the battery lasts so long is that it turns the WiFi off, which is why I had to install Insomnia. It was doing fine so far, with 60% battery, but decided to plug it in since it's getting many requests now