This is just what I needed. I'd hacked one of the USB adapters - mostly because I needed the physical contraption to mount things in - but it drains the battery over time.
The *only* thing I'd add is a 12v connector - the battery has both the 20v and a 12v set of pins on it. For my general use case, 20v was what I was looking for, but every now and then, the 12v would be nice too. (not complaining though!)