Actually, with the extended battery and additional case, mine is 7/8", not 2". Slight exaggeration. I had the extended battery in my Thunderbolt and now in the Rezound. I'm not a fan of the new thinner phones and I like the added width, but I've always preferred larger phones that don't slip out of my hand. I like the way the Rezound with the extended battery feels in my hand. People who complain about extended batteries are usually complaining about the look and often haven't even seen one other than a picture.
Maybe I'm mistaken, but I wonder if you are asking about an external backup battery. I have three 5000 mAh external batteries made by Trent that I got from Amazon for each of our phones. I keep them charged up mainly for those occasional times in the winter when we have an ice storm that knocks our power out for a week or so, but I also have used it when I was stuck at the hospital for outpatient surgery to power my laptop for a few hours because I wasn't near an outlet.
If that's what you are talking about, Amazon has several brands with different mAh ratings and different configurations, some with 1 USB port and some with 2. Just search for external backup battery. For the Rezound, try to find one with a 1A USB outlet. the 500 mA will work, but it will be slower. Also, external backup batteries are one of those items that you often get what you pay for, so I'd go with a good quality one.