Finally a thread on this subject with some real data!
I have exactly the same issue with my Airpods gen2 with wireless charging case in combination with wireless charger Belkin Boost Up (F7U050).
Problem:
It will charge at first, with the "battery percentage" for the case going up at a normal rate.
After a few minutes, the light on the wireless charger turns off (I know that the light on the case itself will turn off after a few seconds, but in this case it is the pad itself indicating that charging has stopped).
Leaving the case on the pad for any amount of time after this does not make it charge more.
The case gets quite warm (I would guess around 40 degrees celsius on the outside) but the pad's light is off (sometimes it's orange, indicating an issue with the object on the pad) and battery percentage stays the same.
What I tried:
* Two different charging pads
* Returned the case and airpods to Apple, and got a new exchange product back.
All with the same result - charging stops after a few minutes.
Also:
* Charging different phones on both charging pads - working flawlessly from 0-100%
So, two different chargers that works flawlessly with other products. Two different airpods and cases that does not work on any of the chargers. This is clearly some fault on Airpods side.
I have even raised this issue with Apple Support, they did some remote debugging but could not give me any solutions. Finally they wanted me to send in the Airpods and Charger to Apple for them to debug. I have not done that because they needed to keep it for multiple weeks which would suck. But it could potentially help to sort this issue out... Anyone that can stand being without Airpods for a number of weeks should contact them.