If you need a backup battery, something along the lines of this may be a good option: http://www.amazon.com/Astro-Ultra-Compact-Lipstick-Sized-Technology-Smartphones/dp/B005X1Y7I2/ref=sr_1_12?ie=UTF8&qid=1410468320&sr=8-12&keywords=battery+usb
It's 2.7oz, and 3200mAh should translate to a little more than one full charge on the new iPhone 6 (from the specs I could find online). I carried a lightly higher capacity version (5000 mAh) on a recent trip to Yosemite and it definitely served me well.

