I've had some success with using an Anker Astro3E USB battery with a few phones using USB Audio Recorder Pro. Using a USB HDD split power cable to connect my Dacport LX to the battery and to my Galaxy Nexus, the battery provides full power to my Dacport LX which is exactly what I wanted! I tried this with my Galaxy S III and to my surprise the battery actually charged the S III while providing power to the Dacport LX as well. Cool! I wonder if that's a hardware or kernel feature..?