Wanted to use the Oculus Go a bit longer than I got with the built-in battery, and got me the Anker power bank: https://www.amazon.com/gp/product/B005X1Y7I2

To feed the power directly into the Oculus Go while using it, I designed and printed a mount for the Anker, connected with a short USC cable (https://www.amazon.com/gp/product/B013G4EAEI).

This mount perfectly fits around the front mount of the head-strap and doesn't move or slide at all. The Anker power bank fits snuggly into the mount and is kept in place by some pressure lips. This keeps the Anker from sliding while using the Oculus Go.

The USB port is on the Oculus Go on the left side, so you probably want to print the left one. However, if one power bank isn't enough for you, there is also the right version. You just have to get a longer USB cable.