All you need is to buy a small lawn mower battery that is 12 volts. Then connect the HID kit directly to the battery via HID Relay. The relay will allow you to trigger from the harness. This way the battery will supply the power 100% and the harness would only supply power to the breaker in the relay to turn on or off.

FYI...O' Reilys has betteries for cheap. I bought a full sized one for like $49.