This is a head mount that allows you to connect the TPCast Battery Box to the HTC Vive with Deluxe Audio Strap (DAS).  This is specifically only for the TPCast.   If you are looking for a general battery holder for the DAS, see our listing here: https://www.ebay.com/itm/264755822813

You are only purchasing the Plastic Battery Holder, nothing else. 

With this design, the TPCast unit itself clips on to the back of the head mount and can remain attached to the Vive regardless of whether the battery is plugged in or not. To attach the battery you simply slide it into the opening on the right side of the mount and it will be guided into place. To remove it just grab hold of it and pull it back out. In theory you can even reach back and swap the battery without removing the HMD from your head (unfortunately since the TPCast batteries aren't hot swappable you'd still end up standing in the dark for a couple minutes while the unit rebooted).

The battery is held in place using the friction from the USB plugs, which is surprisingly quite solid. Even jumping around or turning my head as hard and fast as possible I could not get the battery to come loose. I honestly think you might end up breaking your neck before the battery came off, but if you still don't trust it you can slip a rubber band around the unit for some extra support.

Installation Instructions:

Slip the lip of the head mount over the lower rear strap of the DAS. (The mount may appear to be off-center, this is normal; the mount is designed so that the weight of the battery and the TPCast battery box end up being centered.)

Wrap electrical tape or duct tape around the lower rear strap of the DAS (beneath the padding), and through the groove on either side of the mount. (A twisty tie or zip tie may also work, provided you can get them tight enough).

Thread the TPCast cables around the right side of the DAS. Place the HMD on your head and tighten it up as you would normally wear it to check that there's enough slack that the cable isn't digging into your head.

Wrap the extra cable around the mounting mechanism, in the area between the mount and the back of the DAS.

Clip the TPCast unit into place and plug the cables in. Optional: Use a zip tie or twisty tie to shore up any remaining slack in the cables.

Slide the battery into place, making sure that it's oriented so that the four charge indicator lights are facing toward the front of the HMD.