So I was totally aware of the extended battery being an option on this phone at the time of purchase and I'm now trying to find a quick good deal on this thing. The question I have is this: On ebay I find plenty of well priced sets (I need 2), but I do notice the options are very different. They have like 3 different ones, a 2700 mAh, a 4000 mAh and a 4200 mAh. What is the difference, and what are the risks not purchasing it directly from the manufacturer? Will one of those "cheapos" mess up my phone? sorry this is so long, I searched for quite some time and could find nothing on this particular topic.