Thank you for the advice, i was also considering the original 3100 mAh battery (assuming the one on ibuygou is original) but i don't want those extra 2mm to make the phone bulky. Well i think i'll stay with the standard 2000 mAh for now which gives me a full day of medium-light use.
If you want a battery with more power, it will be bigger. Always. If not, it's a fake.
Ibuygou is completely reliable, I've bought my 3100 battery there and I'm very happy with it.,