If the AirPods are on, and even out of your ears, they don't auto power off, ever. I left them on and sitting on my nightstand all night intentionally, and they never auto-powered off. .
Mine automatically power off, Ive fall asleep with them on 2 nights and after locating them amongst my sheets in the morning they still have plenty of charge.
I wonder if you need to check if yours are faulty.