i have an iPhone 3gs. I bought the phone in November on 2009. I bought a new battery for it back in august 2011 because my phone was shutting off at 20% then 30% then 40%. it was fine for a while. then my phone started shutting off at random. mostly when i use 3g or wifi. now its not really random anymore because every time i use internet or open the camera app it shuts off then wont turn on until i plug it in (shows low battery screen). I'm probably going to buy another battery to hold me over until the next iPhone comes out but i need to know exactly what to get because the last one i got it said on the website and description that it was 1200 mAh and the original iPhone battery is 800 mAh meaning the replacement is better. It lasted only a few months and started giving me problems. thats why I'm asking what to look for and where to look for it. like a trusted site and battery that will last longer than a few months.