I bought two of these about a week back. While I can't and don't don't blame the manufacturer for this, the battery design is incompatible with the very-popular Otterbox Defender case. The plug isn't physically long enough to mate up with the Otterbox-recessed socket. I've gone so far as to purchase an extension cord, because I want to use these batteries so badly. However, the manufacturers of _this_ accessory enlarged the plastic part of the plug itself, making it too wide and long for the Otterbox. So, since it's a major pain the butt to remove the phone from an Otterbox case (twenty minutes and you need some form of foot/baby powder handy, or else the screen fogs) I reckon I'll probably never get to use these batteries that I wanted so badly. (As important as they are to me, the Otterbox is more so.) I'm keeping them anyway, in the hope that I can find a different extension socket or... something. (Ideas and recommendations are welcome.)
The root problem here is a lack of overall standardization; we've got plenty of good iPhone accessories to choose from, but they won't always work together. I don't have a cure to propose for this problem, and I suspect I couldn't use any of the other popular "extension"-type batteries on the market either. But I wanted to warn other Otterbox users that this accessory (like too many others) isn't compatible with the case. I'd also like to ask Giessbach to consider offering an extension plug and cable (with a _correct_-sized plug) as new product line. The Otterbox, I suspect, isn't the only case that this battery (and many other accessories) is incompatible with. I think such a cable would sell well.
I gave the product four stars because a rating was required, and I didn't want to make this product look bad without just cause. In point of fact, I have no experience with it at all beyond trying to force it past the case into the socket while muttering angry words to myself.