I never had any issues with iPhone batteries - I had several iPhones and they all worked fine. Sure, the battery life would decrease over time, but nothing significant. However, my previous iPhone (an iPhone 6) started acting weirdly - the battery would start dying at 40-20% remaining (at least according to the indicator) and the phone would have to be recharged. I tried restoring, doing full charge cycles, nothing. I had that phone replaced and it must've been a faulty component. But that's not the issue here. That iPhone was the only iPhone I charged with my Mophie external battery. One of the features of this battery is fast charging, and it should be ok - I mean, it's even sold through Apple's own site. But, all the other iOS devices I charged only with their own power adapters or by hooking them up to the Mac. The battery issue is probably not related to the Mophie battery, but still, I wanted to ask your opinion. Is using these batteries on a regular basis, erm, safe for the phone - in your experience? I'm sure a lot of you guys and girls use some kind of external battery and Mophie is a well-known manufacturer, but I'd like to hear your thoughts on this.