The PhoneSuit Journey All-In-One Charger is a compact backup battery with built-in charging cables for Android and Apple phones, and even plugs into wall outlets, making it an ideal travel companion.
As long as you don't mind the extra length, the PhoneSuit Elite 6 Pro Battery Case more than doubles the battery life of your iPhone 6.
If it weren't quite so expensive, the Phonesuit Elite would be the go-to option for iPhone 5/5s battery cases. It's thin, light, and can keep your phone charged for quite a while.
The Phonesuit Flex Pocket Charger is a sturdily built, portable battery with a built-in Lightning connector—it'll add hours of battery life, but your best bet for all day endurance is still a battery case.
The PhoneSuit Elite Battery Case for the iPhone 4 and 4S adds more than double the battery life in a compact, classy, and relatively inexpensive package.