The cable that connects the Vision Pro battery pack to the headset for power purposes appears to be fixed in place, but it can in fact be removed if necessary.
Journalist Ray Wong was able to use a SIM card pin to "unlock" the cable, and after he did that, it was able to be removed from the battery pack. There is a small hole located next to the cable, which is apparently a locking mechanism.
The cable that attaches the battery pack to the headset looks similar to a Lightning cable, but it has too many pins to be Lightning. Instead, it is a proprietary cable that won't be able to be connected to other accessories or used for another purpose.
Apple likely made the cable removable so that it can be swapped out without the need to replace the entire battery pack should the cable get damaged in some way.
The Vision Pro ships with one battery, and additional modules can be purchased for $199 each. Each battery powers the Vision Pro for somewhere around two to three hours depending on content. The battery also has a USB-C port that can be used with a USB-C cable for charging the battery, with passthrough charging supported.