Using PwnageTool or Sn0wbreeze for jailbreaking iOS 4 on iPhone 3G won't show battery percentage beside the battery icon in status bar of your iPhone. Acc. to Steve Jobs, some options were disabled in iOS 4 for iPhone 3G to ensure the optimal user experience. However i don't think enabling options like battery percentage will consume much resources of your iPhone and will effect your user experience at all.
Remember: If you will jailbreak iOS 4 on iPhone 3G with Redsn0w, you will get an option to enable battery percentage during the jailbreaking process but it will also upgrade your baseband to 05.13.04 which still can be unlocked via Ultrasn0w 0.93.
Enable Battery Percentage on iPhone 3G Running iOS 4
- First step is to install iFile on your iPhone / iPod Touch. You can find step-by-step guide here for iFile installation on iOS 4.0
- Open "iFile" and and go to "root" directory. Tab on top left corner of your screen, it will take you root (/) directory.
- Go to /System/Library/CoreServices/SpringBoard.app and look for N82AP.plist file.
- Once you will open N82AP.plist file, you will see the coding regarding your iPhone functions, you will need to edit the file and add "Battery Percentage" function to it and set it to "TRUE".
- Tab on "Edit" on top left corner of your screen.
- To enable Battery Percentage add following strings to N82AP.plist file.
- One you are done with adding these strings, just tab on "Save" and "Done" and close the iFile app.
- Restart or respiring your iPhone 3G and now you will see numeric percentage of your battery beside the battery icon in status bar of your phone.