Here's a quick look at the Samsung 9000 mAh external battery pack that came out this spring and is currently available from the fine folks at ShopAndroid.com. These sorts of Android accessories are pretty simple by design, and Samsung's done well here. You've got a blocky charger -- it's about the same size as a deck of cards, but thicker -- but with sloping edges, making it easier to hang onto, if for some reason you don't want to stash it in a pocket.
Functionally, there's not a whole lot to do here. It blissfully charges via microUSB (this wasn't always the case with older batteries) at 1.8 amps -- that's the rated output as well. There's a real on/off switch instead of a button, which we prefer over pushbuttons. Four LEDs indicate the battery's level while charging or discharging. The rate at which your phone will be juiced up depends on your phone's battery capacity, of course -- and some phones like the HTC One may charge slower on purpose. But we didn't notice anything untoward here. It just works.
Samsung's included a short USB to microUSB cable as well as USB to 30-pin cable for charging Samsung tablets. (Smart!) You're on your own to charge the battery up, though, as there's no wall charger included. That's not a big deal, though. Chances are you have at least one laying around.
The one downside -- this sucker's not cheap. At all. But then again, it's got an expensive brand name on it.