I don’t have or use AirPods, so take this advice with a grain of salt.
Sometimes charging issues can occur if any contacts get corroded. I’d get a cotton swab and dip it in isopropyl alcohol and give the interior a solid cleaning. Let it dry and try again.
I don’t know your location, but humid environments are rife with corrosion. Also, it could be that AirPod quality control has been shit lately.