Dan bought an iPhone 6 and he loves it, but he needs more battery life out of it. He's looking for a good external battery, but is overwhelmed by all of the options. Leo says unfortunately the iPhone has no removable battery, which is the tradeoff for it being so thin. The iPhone 6 battery life is better, but with the larger screen, it needs more juice. That's one of the reasons Leo likes the Samsung Galaxy Phones -- he can swap out the batteries with a backup. Many people use Mophie Cases, which have a battery built into them. But they make the phone quite a bit larger.
External batteries are a good option. He'll want one that has a decent mAh, like 5,000 mAh, which would be enough to charge the iPhone twice. Leo likes Anker and Jackery when it comes to external batteries. The Jackery Giant is a good one.