12 volts will NOT run a 120 volt HID light. For one thing, battery current is DC, the lights require AC. So you need some sort of converter. One car battery isn't going to power you for very long either. You will have to keep recharging them, which would just be a pain in the ass. I hope you're not planning on using regular old incandescant light bulbs because those won't work. I think you need to do some reading and research before you jump into this