I use a camera that runs on 2 AA batteries and I always carry spare batteries.

As for a GPS, I recently got the Pocket Earth app on my iPhone. I downloaded the country maps and, without a data plan but with the phone connected to the local cellular network (I had foreign calling set up on my phone but didn't use it--emergency use only), the GPS in Pocket Earth showed me exactly where I was. No data plan required.

I tour in developed areas and always manage to pass an electrical outlet at some point in the day. If necessary, I spend extra time sitting around to charge a depleted phone.