My airpod pro takes a long time to charge, and it's not even fully charged in more than 8 hours

It's been a while since my airpod pro case takes more than 10 hours to charge. I sometimes need to unplug it and plug it in again to continue charging. My charger is the original 20 watts apple charger and I charge my phone with it and there is no problem with that. The airpod is still in warranty time. What should do?