Skip to 25:50 to see the end result.
This is simply a build log of bodging batteries onto a TrackIR proclip instead of the cable, making it cordless.
UPDATE: After a little less than five days of continuous operation where I simply never turned the battery pack off, I was down to 4V on the pack. The diodes are then so dim that the TrackIR camera has problems seeing the light when I turn my head very far to the side.
I will call that a success and probably make a better head mount when I get the urge.
