mobile

It seems that my battery started dieing, i know software, wakelocks and app usages, and i get Galaxy S3 performance out of my battery, way lower then it should, tryed factory resets, different firmwares, battery to 0% then 100% on shut down phone so it can reset its self, nothing helped. I have it since november and i'm a really heavy smartphone user, some of my friends are saying its not possible to deplete the life of my battery so fast but maybe i did, now where can i buy an original battery? Im from Macedonia so i need a reliable source/shipment/store online, can anyone help me/point me to a link? Thank you in advance