I have a Kensington battery which works great. The only thing I would change if I could is how it charges. It uses a micro USB to USB cable to charger. I am looking to get a battery for my friend, but would like to get her one that charges using the Apple dock connector, and even better would be if you could connect it in between your iPhone and computer and sync through it. The Kensington one does not let you sync when you connect it to your computer and iPhone, only charge. I've been looking around the web for something like this, but haven't been able to come up with anything. I was hoping someone here has had better luck than me. Thanks.