So I thought I'd share my experience with buying an extended battery for my Galaxy S3.
I got my phone about three weeks ago... I completely fell in love with it, except for one small flaw (at least for a heavy user like me...) - the battery life. If I conserved my battery by managing brightness/radios, using power-saver mode, forcing my phone to use HSPA+ rather than LTE, and had a fair bit of luck, I could charge it before I went to bed and last up to nine hours. Although I could make it work, I figured there had to be an easier way...
So I did a little research and found the QCell 4200mAh extended battery on Amazon. I was definitely skeptical at first, but this was one of the only extended batteries I saw that supported NFC (not that it was a huge deal for me anyway...). So, I hoped for the best and bought it for a little over twenty bucks.
Once it arrived, I popped it in hoping to see improvements instantly. Although I could tell a little bit of a difference, it wasn't much; however, I remember the product page saying something along the lines of "the battery won't reach it's full potential until it has been through five or six full cycles). A week later, the extra battery life began to really show. The other day, I managed to get eighteen hours of battery life, with a 26% charge remaining. This particular day, I left my screen on full brightness, left LTE and WiFi radios always on, kept haptic feedback and vibration on, and even had the GPS running. I didn't even have to use the power-saving mode! [note: I didn't use the video player or play many games this day, but it was still a huge step up]. I would have kept going to see how much time I could really squeeze out of it, but unfortunately I had to wake up early for work the next day, so I just let it charge. Whenever I get a free day, however, I'm definitely going to push the battery to it's limits with games and videos.
If y'all have anyone questions about the product, let me know! So far, the only minor complaint I have it the Blue back cover for the extended battery doesn't look nearly as nice as my original Pebble Blue backing, but it's worth it.