intocircuit

tl;dr: Slightly pricey, but it'll be worth it when you need it!

I've carried a small external USB battery pack with me for the past few years, ever since I started relying on my iPhone as my only camera, phone, reading device, and emergency-backup-Internet device. And there have been many times where I would've been up a creek (or more literally, lost in the middle of an unfamiliar city!) without it.

But the little battery pack I tote around is only really for emergencies—it can barely top off my iPhone when the phone is already at 50% capacity, and if the iPhone gets below 10%, it'll struggle to even maintain the current charge if I have to use the iPhone while charging!