I had to return the first one that I bought as it didn't work at all, so this is a review of my second one. It started well, after fully charging it I plugged it into my iphone and this time it was recognised and charged the phone. I fully charged the Pebble again a few days in advance of a long train journey as I wanted to use it to boost battery power. On the way back I started charging my phone and I was pleased to note that I could still use the phone whilst charging (for apps not necessarily calls). Anyway I got interrupted half way through charging and had to stop for about 10 minutes. When I plugged it in again still on the same journey, the Pebble was not recognised at all! I tried a few times and then assumed that it had broken and was all ready to send it back again. This left me still on a long journey with no Pebble again, although my phone had been part charged. When I got home I thought I had better just see what happened if I fully charged it again, and lo and behold it started working again. I am assuming from this that the Pebble will not charge a phone when it is not almost fully charged itself. Therefore beware of any charging interruptions (make sure you go to the toilet before you leave the house!) or you will be in trouble. Like most gadgets of its kind it also loses charge whilst sitting around doing nothing, so you will also need to fully charge it just before you need it (not always possible if you don't know when you will need it). Also quite a few people have complained about the sock to hold the Pebble saying that everything falls out. I just use a safety pin at the top and it holds everything in. Anyway, my title sums it up, great little product when it is working, but not exactly reliable!