This is exactly what I've been looking for - and it works fantastically!  Very simple to use after initial 7 hour charge.  It relieves anxiety about my iphone 4 running out of battery power when I can't get to an AC outlet.  I take it on trips and never have to worry about my iphone running out of battery power.  The battery pack also holds a charge:  for example, if I fully charge it before I leave on a trip, it will still retain power after numerous days of non-use, and then I can simply re-charge it.  It's a great price for a very priceless product!