There is NO handcrank GPSr. Most GPSr do not have the circurity to charge the GPSr, although you can run the GPSr off of external power it woll not charge it. You could use a amall solar power unit to charge a set of NiMH batteries so you would just be rotating the batteries. This would be the best option. Also you do not have to keep your GPSr turned on 24/7 so just using it periodically your save batteries. But the solar battery charter would be your best bet.
cheers