Why does my AirPod battery drain when not in use and inside of the case?

I had a similar issue, when i take my airpods out of case one of them was 100% and the other one was around %40. As i put it back to case i have noticed that it was not charging. I have blew both on airpod and case to remove any possible water or dust and put the airpods back to case, and they were charging back.

My recommendation could be blew inside the case and the airpods.

Regards,

Each AirPod along with the charging case include a Bluetooth part which remains on to provide instant connection as featured, therefor utilizing your battery life even through standby periods when the AirPod or Charging case is not being utilized.