The battery on my iPhone 3Gs (as I hold out for the iPhone5) runs down within an hour if I use Pandora, Instagram and email. For months I walked around with the charger cable in my bag, trying to find an electrical outlet whenever and wherever I could. Sometimes that's hard to do in NYC. Now I have a better solution - I carry this around, plus the cable, and it doesn't matter if I can't find an electrical outlet. Just taking the subway to work can result in my phone fully drained by the time I arrive.....but now I can keep it fully charged while I commute.