Just a quick and dirty adapter to power your Quest while connected to the PC using a Link cable, allowing for the full 3A output of an Anker battery, or the 2.6A of a BoboVR B2 battery. Basically, you want to bypass the power leads from the cable's input connection, then connect the leads of another cable to the power leads of the connector feeding the headset. This image gives the rough idea...
With the USB-C cables, there's obviously more wires, but they're wrapped in foil, leaving the power leads separate from the rest so it's easier to handle. Simply cut the sheathing of your main cable where you want to make the splice, then cut and strip the red and black wires, leaving everything else as is. Then take your other cable you plan to inject the power with, then cut the cable to length. Then strip the sheathing, and cut all wires except for the red and black power lines. Then strip the tips of the red and black wires on both cables, then solder the 2 cables together, making sure the red wire on the injection cable is only soldered to the red wire on the main cable that leads to the headset. The other half leading to the PC should not be connected. Then connect the black wire from the injection cable to both halves of the black wire on the main cable. Use shrink tube as necessary, or electrical tape. After that, you have power from the external battery, as well as data connection from the PC. You should never run out of power in the headset after that, unless your external battery runs empty. 😋
The cables I had on hand seem to be discontinued, so I'll link some alternatives that are a bit longer, but will allow for the Link cable to connect behind the headset, as well as allow for direct plug-in connection to the external battery. With the cables I had, I have to connect both Link and power cables on the side arm of the headset, and my power injection cable has a female port, but works great with the BoboVR battery dock. It still works quite well, but I'm ordering the longer cables as well.
Have fun. 😎
https://www.amazon.ca/dp/B08NNM96PY
https://www.amazon.ca/dp/B07QYRB1YW
https://www.amazon.ca/dp/B08XXGNJHG
Alternatively, instead of powering from an external battery, you could also design it with a male connection to the PC, then a female connection to the Link cable, then just the Link cable connects to the headset, with the adapter acting as a powered hub. Just make sure to disconnect the red power line to the PC. You can then power using a 5V/3A wall wart power supply, like an official Raspberry Pi 4 5.1V/3A power supply with the USB-C connector. I'm just not sure how much voltage drop there'd be over a 10+ foot Link cable, as well as the 3-5 feet of the wall wart's cable.
Edit: You could always modify a SATA power extension cable using just the 5V and GRND lines, then modify a PCI slot cover with a USB-C female port, then a cable from the port to the power injection of the Link adapter. They can handle 3A.
