Earlier this year I bought a backup battery for my iPhone at the airport on a snowy day right before I got on a plane. After the second hour of sitting on the runway (snow in Seattle creates havoc) I felt like I was a genius for getting the battery. It also saved my sanity during several hour long delays on the way home at the end of that trip. I chose the Mophie Juice Pack Powerstation battery because it holds about two full charges and, this was most important to me, it connects to the phone with a cord instead of sticking directly into the phone which means it is easy to keep using the phone while it’s charging. It does have it’s own cord for charging the battery itself (it has a USB end so you can charge using the iPhone’s convertor or your laptop) which means carrying around the battery as well as the extra cord. I’m happy to make the extra space in my bag because it means I never have to fret over whether my phone is charged as I’m heading out the door. It’s like my pet, I should give it a name. And, oh hey, according to their compatibility sheet it will also charge our Kindle. You can also find it on Amazon.
I had also considered the Mophie Juice Pack Plus, a battery built right into an iPhone case. It’s convenient because you don’t need to pull out anything, you just turn it on. But I’m too in love with my squishy iPhone case and being able to scrub said squishy iPhone case with soap and water periodically to give it up.