I don't think 5W is too far off from what this thing draws under load. I have a 10,000mAh ~4.2V battery in it, and I get about 10 hours of life. The battery is

I don't think 5W is too far off from what this thing draws under load. I have a 10,000mAh ~4.2V battery in it, and I get about 10 hours of life. The battery is clunky, 9.6mm thick, since it was originally intended for external phone battery packs.