" battery would be dead quickly without being plugged into the car's power source."
I would expect that, Fortunatley, It can be plugged in in the car.
The issue with Sygic was that it was sucking up battery when I wasn't using it. The app wasn't running (as far as I could tell). As long as the app was installed, it was high on the battery use list.
NavFree doesn't do that. I've got to try it out on a long trip this weekend.