One other general comment about phones - they don't like to get wet.
Problems solved. Battery life of 8 hours on the external pack (8 nimh 2500mah) running through a car usb adapter.
The case is water "proof" to the point that it will hold off a rain storm for an hour or more - I've tried. The touch screen works through the window and the booster battery will sit underneath the phone. Total cost to build around $30.