I am a previous user of the Apple Smart Battery cases. I have a question that I can't seem to find the answer to. It seems its intent is to snap it on and charge up the phone really quick if you need some juice. Previously I have used the case, and obviously with the case it charges your phone up to full capacity then draws from the battery in case first until depleted. Does the battery pack work the same way, or does it charge it up then stop?