The New Trent battery pack is lightweight and small, and works easily and well.  My only beef with it is that the 5000mAh rating may not be accurate.  I compared it to a Zaggsparc 2.0, which is rated to same capacity, and the Zaggsparc clearly carries more "juice."  However, Zagg's product is more than twice the cost!  So, for my money, this is the better buy.  The charging cables it uses can be a bit more cumbersome than some other options out there, but the cable is retractable, which is nice, and again, it's a much better price.  If you're looking for something to extend the usable battery life of your smartphone, this is what you want.