Right now I've got it hard wired in with a car adaptor spliced into a 12V source, unfortunately if the car is not running there is not enough power from the adaptor to run the external usb hard drive. And the PC will constantly switch from AC to battery modes, with the pop up constantly flashing on the screen. Pretty annoying. One of the most frequent thing I use the PC for is to flash different tunes to the cars ECU, or to check the ECU learned history for fueling and timing. This requires the ignition to be on, but the engine off. So while I do this I constantly have it switching from battery to AC.