Newer Version HERE: https://www.thingiverse.com/thing:4644601

Don't buy the $130 Elite Battery Strap. Instead, clip a 10,000mah battery to the back of your quest with these because it's cheaper, triples the battery life, and more importantly is an even better counterweight.

To complete this project, you'll need:

• Two of these clips
• A 180-250 gram battery capable of 5V3A output
• Some sturdy velcro (or 3M Command Strips)
• A 1.5ft cable that fits the battery you have.

The clips slide on from the side and so that you have a flat surface for you to velcro any battery on, and are easily removable.
The battery I recommend is the $20 10,000mah Aukey with passthrough charging that has USB-C on one side and USB-A on the other, so that you never need to unplug the battery from the Quest 2, but for some reason it's not always available: https://camelcamelcamel.com/product/B08H8KKW5Q

But any battery with a flat surface should work, including the other slim 10,000 mah USB-C Aukey that's on Amazon.

From my experiments, a battery that was 250grams would let the fulcrum of the entire headset be centered right at the top of the head. Anything more than that will feel back-heavy, and anything too much less than that will be an insufficient counterweight.