Apple is researching ways that other devices such as straps or even AirPods, can charge an Apple Vision Pro while in use.
Right now, the only way to keep using an Apple Vision Pro uninterrupted is to have to plugged in to a wall socket. Under battery power, it lasts up to around two hours, and that battery is not hot-swappable -- the headset can't carry on working while the battery is changed.
Or it can't at present. A newly-revealed patent application called "HMD with Charging Device" proposes that an Apple Vision Pro could be "charged using a wearable electronic device." While the patent application is typically vague about that wearable device, it is clear that it would "magnetically connect... to transfer power."
While the text is as consciously unspecific as all patent applications are, the drawings with it are much less so. All illustrations that show any device being attached to the Apple Vision Pro appear to be showing AirPods.
Detail from the patent application showing AirPods being moved from in-ear to charging the Apple Vision Pro, or at least a slimmer version of it
The drawings are all simplified diagrams so that can't be certain, but these charging devices are show at around the size of an AirPod. And they're also shown being first worn in the user's ear. In this case, the diagrams imply that the user can take out an AirPod and magnetically attach it to the Apple Vision Pro.
Given the tiny, tiny batteries in any AirPod, that would seem sufficient to charge the headset for about as long as it takes to change the main battery. If you're lucky.
Patent applications almost never consider use cases very much, though, as they are always focused instead on how something might be achieved. So for the purposes of the patent application, being able to connect an AirPod to charge an Apple Vision Pro is sufficient.
If this is ever to become an actual product, however, that AirPod battery is surely inadequate. So while the patent application does not cover this, it's a reasonable assumption that Apple is looking at other wearable devices.
Right now there aren't many, with really just AirPods and the Apple Watch. It's no more likely that the expected Apple Ring will have a big battery than the AirPods do.
So unless there is some as-yet unimagined new Apple wearable, the most likely possibility is that an Apple Vision Pro could have a strap that contains a battery. There hasn't been a precedent for this yet, but there has been a clue in the form of the Apple Vision Pro Developer Strap.
This is a $300 Apple Vision Pro strap that replaces the right-hand audio assembly on the headset. It lets developers connect the Apple Vision Pro to a Mac using a USB-C cable.
So at least Apple has already released one replacement strap that does more than help keep the Apple Vision Pro on users' heads. Maybe this patent application truly is pointing to a future strap that does more.