Originally Posted by
RC28 p2kart and wrxnfx that makes sense. However if the battery is at 100% or close to it, it should power it without charging it. The external battery I have says using it is one way to save and prolong your battery. I am not sure if that is just marketing hype.

Without knowing the circuitry, we probably won't know for sure. If the battery is bypassed at 100%, it is possible that the external pack would take over. This does make sense. I'm wondering if it truly is this way only because a lot of people say that docking you phone extended periods would damage your battery. The phone is not setup to know the difference between wall charger, external battery, etc.