Up to three charges for iPhone 4
This is a great device to have as backup storage for your gadgets. I went on a four day backpacking trip and used this device to charge my iPhone 4 at the end of the day. I was using my iPhone 4 as a GPS tracker and I completely suck through my battery with one full day of hiking. The power device was able to hold enough charge to charge my iPhone 4 from dead to 100% three times and it only took a few hours to do so. The power device is extremely small and lightweight, so it wasn't a nuisance at all to carry with me on the trip. It's about the size of a typical male wallet. I haven't tested the durability or water-resistance yet.