I bought two power packs from mymemory.com. I got one each for myself and my daughter for our iPhones. I have tested them several times at home and they give a full charge to an almost dead battery. I also used it yesterday to charge my electronic cigarette battery while to see if that worked and it was fine. They cost £4.99 each and are about the size of a large Pritt stick. Very happy with what I got for the money. The only thing you need to remember is to have your data cable for your phone with you as you will need that to connect it to the power. Or buy a spare cable if you think you'll forget the one you have.