My iPhone 4S tends to go through the battery fairly fast.  I am on 4G often (work wifi is bad), so I tend to need a lot of juice.  The iTorch IMP52D certainly has that.  I started with the NT52D, which is a lot larger (pack of cigarette sized) and had the same capacity (5200 mAh), so the size of this one is nice (more like a big lighter).  It fits in my pocket better, or in the side pouch of my backpack.  When I do that, I can have the backpack on and have the phone on a 6-foot cord, charging as I use it.  Very tech-geeky.