My old work provided iPhone 4S has been having annoying battery issues.
If I do something power intensive, like run Google Earth, when the battery is at 50% or so, the phone will shut down and say the battery is dead. So I plug it back in, and it turns on again and says everything is just fine. It has 60% power and all is good in the world. No big deal unless I'm on a hike, or camping or something and can't charge it.
So I just bought a myCharge AmpMax power supply. It's pretty cool. Smaller than a deck of cards. It has a female USB port, so it will charge any device with your provided cable. They give you another cable so you can charge it from your USB power source (wall wart, car charger, laptop, etc.)
It's supposed to be able to fully charge your phone 2-3 times before needing to be recharged itself.
One more thing to carry on those trips, but not too bad.
