Battery Low Problems with the SIII !!!!!!!

Hello to everyone, my problem is that one night i left the i9300 charging but I forgot to lock the screen and was all night the charging but with the screen on, when I get up an see the phone was extremely hot and freezed, the first I do was get out the battery and leave the phone 1 hour for decrease that hotness and since this day my SIII is crazy, sometimes when ts about 50 % of battery turn off r reboot himself, automatically at 20% go to 0% and when i'm playing for 15 minutes seems that the GPU fails and turn of after the screen shines turns off but ager testing was the battery so anyone knows any lace for bought ann original samsung battery in a good price? Thanks