You could be pushing the M1 a bit far with that lot especially the 12v line but you don't say what kind of HD you are using. Is it a desktop or laptop drive? You might also have some volts drop in there so running the main power from the battery is always a good idea. You can check this with a digital multi meter if you have one. It might also explane the hard shut down when the engine isn't on or that could just be the battery is on its way out or just isn't big enough. A meter will tell you what's up.