Airpod case will not charge past 7%

the airpod case I had all of a sudden would not charge past 7% even while it was charging. I though I'm just going to let is fully die and charge it, but after the battery hit 0% it would not charge anymore. The airpods in it would but not the case it self. After getting a new case 3 weeks ago it is happening again. The exact same thing is happening. It is not charging past 7%. Is this a problem with my phone the airpods of the case?