Thanks Simon.
How did you get it to blink when the voltage was low? Also - do you know if the regulator will operate at 7.2V input? If I put in six 1.2V 2200 mAh rechargable batteries, I could have something that's good for long-time road use.

Also - I am going to convert my old patch cable to work on the 12V - 14.4V in the car in case I want to do some extensive GPS/mapping stuff that requires external storage.