I bought this last time around and it worked well for the battery charging - it charges fast, but it does get rather warm. It will charge my 5 about 2.5 times before it needs its own boost. A couple negatives -
the earphone jack is so far recessed and the hole to get to it is an unusual size/shape so I have to use their adaptor. Which was no problem until I lost it on an airplane. The other problem is the case is extremely slick - I dropped it almost as soon as i started using it and it protected my phone BUT the case broke. Because it is slick plastic, I dropped it more than once and the breaks continued. Now I have it patched with little pieces of gorilla tape. It is so slick I thought about putting some of those bathroom tub anti-slip stickers on it to add to the grip It uses a mini usb plug to charge, so that may be problematic for others, too.
I wish OTTER BOX made something like this - we have had no problems with those over the past 5+ years.
All that said, I am going to order another one and try to hang on to it better.