This is my first post on xda ever!
I'm currently into that topic... I tested one battery a few days ago claiming to have 2680mah capacity! It says something like Gold battery bla bla... Well I DON'T RECOMMEND THIS BATTERY! It has nowhere near that capacity... It is even worse than the original... Right now I have another one from a company called "extremecells". They are making a promise on their homepage saying that if you find another battery of the same size with more real capacity than theirs, they would give you 100€! And that counts for all of their batteries... Well I ordered one 1750mah BA800 battery which I use right now and it is already much much better than the one before... I ordered another one from a site called batteryupgrade.com (or. org or something). There is a battery from Max Power claiming to contain 2100mah! That one is still on its way to me... I will keep you updated on that one when it arrives!
For now I can recommend the battery from extremecells!