Although the Syncbac PRO can be used to pass power through to the GoPro HERO4 and GoPro HERO7 Black*, when the SyncBac PRO is connected to an external power source, the GoPro's internal battery must remain in place.
In order for the Syncbac PRO to work reliably with the GoPro camera, the communications element of the GoPros subsystem requires constant power, which is dependent on the internal battery.
Removing the internal battery will prevent the SyncBac PRO from communicating effectively with the cameras' media files.
* Due to limitations in the GoPro HERO6 firmware, this feature is not enabled for this camera model. More information available here.