I purchased an "Emergency Phone and iPod Charger" yesterday from Autobarn. It was on sale for $6 - apparently, the "normal" price is $20.

It came with an assortment of connecting cables, including a mini USB. I loaded a AA battery into it (not included), and connected it to the GT-11. Worked a treat! Intended phone usage now completely forgotten.

Might be worth carrying one in your kit, just in case.