Low battery runtime, and occasional audio lockups are well known issues...if you'd read the release info you should be aware of this.
There is nothing (probably) wrong with your battery, if there is, installing emCORE and/or Rockbox didn't cause it.
Freemyipod has clear resources detailing both installation and removal of emCORE and Rockbox, as its emCORE you need to remove (which will in turn uninstall Rockbox completely) it would be best to contact them directly.
However, I'll clarify here:
i want to get the originl apple firmware again and ive searched over google to solve my problem
How much searching did you do to solve this issue exactly?
A google search for uninstall emCORE+iPod Classic
gives you exactly what you need as the first hit...
Warning: Uninstalling emCORE will delete ALL data on your iPod Classic!
1. Install iTunes on your computer (if you don't have)
2. Connect your iPod to your computer
3. Press and hold the menu and select buttons for between 10 and 15 seconds (The iPod starts to reboot after about 5 seconds, keep holding the buttons until it seems to turn off completely). The display of your iPod should now stay black, and a new USB device called "USB DFU Device" should connect to your PC.
4. Restore using iTunes