Interesting that this was (is) the first (readily) available iPhone - compliant (WWi approved) backup battery. Again with the blurry! Damn. 
 
 
This is pretty standard stuff ... 3v to 5v boost. Not sure of the overall efficiency, but it does work down to about 0.5v. That would be a far stretch, as 2 AAA batteries would be considered dead at about 1.8v. Battery life would depend greatly on the state of the iPhone, but 1-2 hours of talk time is reasonable