This charged my iPhone 4 from 10% to 100% in 4 hours on 4 duracel AA batteries. I bought this as I'm going camping soon, but am not convinced its going to do the job. When the phone was charging, it kept churping and flashing the apple symbol on the screen, which was a little worrying, although it did charge and the phone is fine. I think 1 charge has about killed the duracell batteries, which could make it quite an expensive way of charging the phone. So I'd rate it as "OK", not as good as I was expecting.