GTMax 5000 mah Battery
GTMax White 2 USB Port External Rechargeable Emergency Backup Battery Charger for Sprint Samsung Epic 4G CDMA
I thought this might help some one awesome 5000mah battery just use some velcro and have extra power without an outlet possibly for 4 days.
a better solution might be more http://tinyurl.com/23q6k6m
Used the phone for 10 hours running GPS and taking some photos and the battery died. Not the 4 days of power that I hoped for. Unless you use it conservatively. After the battery died I still had fully charged cell battery which lasted me a little over 3 hours running gps.