Hey Atakan24,
Thanks for posting in Apple Support Communities. We understand that the battery widget on multiple devices shows your AirPods case at 0% until you place the AirPods back inside. We'd like to help!
If you haven't already, reset your AirPods. This is an easy steps that can help resolve unknown issues: How to reset your AirPods and AirPods Pro - Apple Support
You mentioned that this occurs on multiple devices. However, if a reset doesn't resolve the issue try removing the battery widget before restarting your iPhone and testing again: How to add and edit widgets on your iPhone - Apple Support
Let us know the results! Take care.