I mentioned this in a previous post a while back. I have done many tests and found that is a proven fact that it will not boot if it is too cold. Once it has been warmed up, either by leaving it plugged in for a bit and running the car, or even sitting on it for a bit, it will work just fine. The last time I said this, people shot me down mentioning temperature thresholds and such saying there is some other problem. I don't know about any of the technical specs ot thresholds or any of that, but I have proven on many occasions that this thing will not boot if it is too cold. So now I leave it plugged in at home so it's warmed up and ready for use when I take it out to my car.