Battery/Case Combos?

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I think I might be interested in having a case with a battery of its own, to extend the life of the phone's battery. (I seem to remember something similar for the iPhone).

Any recommendations? Options?

I haven't seen any droid x/x2 specific external batteries, but I have recently seen the Trident Electra Case and Extended battery. It was recommended to me on Amazon and it comes with a 3200 mAh battery (double the standard x2 battery size). The only thing is that this case is a freaking BEAST, check out some videos on it.