Dear Hoflandhome,
The charger you are using has a specification of 5V/2.1A, and the current has already exceeded the range that the headphones can handle, which may affect the charging effect or even cause minor damage to the device.
We recommend that you switch to a standard 5V/2A charger to try charging again and avoid using the fast charging mode of your phone. This will ensure the safety of the headphones and smooth charging.
We hope you can use them successfully after the replacement. If you have any other questions, please feel free to let us know.
Best regards,
Lin