Does anyone have any experience with any of the high capacity replacement batteries that are available online for the iphone 5? It seems like the same one is listed for sale on several different websites, but I'm extremely skeptical of these things for obvious reasons. Are they all fake? (they claim to be 2680mAh) I've been using both the Mophie Juice Pack Air and a Maxboost Hybrid and while both have their positive attributes, I would prefer to not have to carry such bulky cases. Replacing the internal battery with a higher-capacity battery would obviously be ideal, but I've never heard of anyone doing it. I guess these batteries don't live up to their claims? Or maybe nobody wants to void their warranty by trying one?