I own this battery, and it give you a real noticable difference, the stock battery is rated at 1500mAh and this is 3300 mAh, so you would expect, logically, a little more than a 2x increase in battery life. Ill let you know that it will let you extend into the 3rd day with your average web browsing, simple games (ie. words with friends) mms, and of course, phone calls. I have pushed the phone into the 3rd day. The good news it it gets better and better if you get a good kernal for the epic 4g that has the potential to save battery un noticeably.
Sorry for the spelling mistakes,