I thought i'd say that according to a lot of people these same size large capacity batteries are pretty much standard batteries bought cheaply with a fake mAH on so they can make an easy profit. A lot of people have bought them and not noticed any difference. Im referencing the Darky ROM forum; and if you see here i think there's talk of that.
Also that link is a topic for an 1800mAH battery that according to many people in the thread, actually makes a nice improvement (and its same size.) Try looking there, seems legit.
Just wanted to say i would be carefull to use any ebay batteries.
I got a extra battery 1500 mah with a sgs package i bought.
So wanted to try the battery, put it in the phone and turned phone on, worked and it had 25% or so, so i put it in the charger and 2 hours later i came to see my screen messed up, lots of white and black lines , looked so horrible i tought my screen was ****ed. Luckely when i put my original battery back , the phone did actually boot up and the screen works fine . Won't ever try a cheap ebay battery again