Hot Swap powerbank system
Here is my take on the hotswap powerbank system. Uses cheap lightweight VEEKTOMX batteries, beloved in hiking communities. They have sufficient output to keep the internal battery topped up during active gaming. I haven't timed it precisely, but one powerbank gives you approximately extra hour of gameplay. If you get three-four of these, you should have unlimited playtime.
Powerbank weighs 213 grams, and the holder itself is 38. Including cable, total added weight is a bit over 250 grams. It's not unnoticeable, but the balance is OK. The biggest difference is that there is more inertia when swinging your head, since the added weight is unfortunately positioned away from your head.
USB-c cable is permanently attached with hot glue. This is a sacrifice I'm willing to make :)
On the flipside, it is true hotswap. You can even swap the batteries without taking the helmet off.
Here is the model on Printables, there are also more pictures. And if you want to fiddle with the design, it's available in Onshape.
This is the battery on Manufacturer's site; it also has a link to a listing on Amazon.
Unfortunately, the current generation model (with two USB-c ports) is slightly larger than the previous generation (with USB-c and micro-USB). I have a bunch of last generation batteries, so I designed for them. However, updating it for the new generation should be fairly simple - I'm planning to do it within a few days, I already have one current-gen battery.