Oh, I forgot to say, you need good thick cable to connect it to the battery, and keep the cable run short. When first powered up they have a sudden current draw (I think they charge a capacitor which then has enough grunt to fire up the compressor). This sudden current draw can cause a voltage drop if the cable to the battery isn't a generous enough gauge or is too long, and that causes its automatic circuitry to assume it is about to kill your battery so it shuts itself down - I got fooled by this problem when I first installed mine.
Steve.
