I started with a Mophie on my 3gs, but after it died i switched to cheap Chinese models. I am still using ones from China ordered on eBay. I have supplied them to family and friends. I usually pay $8-15 dollars apiece. I have a external battery attached to my iphone every day. The mophie is only a 1500 mAh, most of the Chinese are 1900, and some are 2100.