Sketch works when powered by USB... 12V battery doesn't work?

I'm using an arduino in a robotics project for my senior design. The sketch works and runs fine (as well as it can with my ghetto design) when I am running the arduino from the USB port. However, when I tried hooking the Vin to this battery:

and the negative to ground, the arduino turns on, but the servo does not move. I can't tell if the sketch is actually running or not, but the arduino's light is definitely green. Can someone help me out with this?

Edit: As it turns out, I apparently have to press the reset button after connecting the power... strange, but whatever works.