S3 battery not work after water damage I dropped my S3 in water and the stock battery stopped working. I didn't know how to fix it (I tried drying it with a hair dryer but it did not work) so after comparing prices and discounts I bought a new replacement battery from MPJ and have used it for a month already.

It appears to work just as well as my stock battery. I don't know it's actual longevity but it works OK so far. Since I ordered from an official website, hopefully it's not a fake one...

I still want to fix the stock battery though, can anyone help me?
Basically, you can't. The charge/protection circuitry in the battery probably got damaged by the water, and you're done now. 

Count yourself lucky that it was only a new battery that you needed and be happy.