Mophie would probably argue that the Juice Pack Pro is actually tougher than an Otterbox case. It's touting its first ruggedized battery pack case as exceeding military specification MIL-STD 810G, which is pretty tough.
That said, the case is water-resistant but not totally waterproof (it can't go underwater). It has a built-in screen protector and comes with a rotating belt clip. According to Mophie, that 2,500 mAh capacity battery provides 150 percent extra battery for the iPhone 4/4S and is the largest battery case the company currently offers.
Other features worth noting: the included USB cable enables simultaneous charge and sync (with iTunes), and an on/off toggle switch lets you choose between standby and charging mode. Like other Mophie battery cases, an integrated four-LED status indicator lets you know how much "juice" is left and also displays how much time remains during the charging process.
Needless to say, it's not a lightweight case (the shipping weight is listed as 1 pound) and it is rather pricey at $129.95. But for those who want both a seriously rugged case and a built-in battery extender, this will definitely be on your short list.
As soon as I get my hands on one, I'll let you know just how bulky it really is.