I wouldn't use a battery powered unit in your vehicle. You can just about guarantee it will have a dead battery when you need it most out in the middle of nowhere. One that lugs into a 12V accessory outlet (cigarette lighter for us old guys) or clips to the battery directly is much more reliable at any time IMO...
I agree. If you have a flat and a dead car battery, time to call for a roll-back tow truck.
