To jailbreak iPod touch, check this tutorial.
Steps to Get Battery Level Percentage on iPod touch 2G/3G
1. Open Cydia, tap the Search tab and search for ‘SBSettings’.
2. Install SBSettings app. Now open Settings where you’ll see SBSettings. Click on the ‘More’ icon. Open System Options and Turn ON the ‘Numeric Battery’ option.
The battery level in percentage (%) will immediately appear next to the battery status icon.
SBSettings is a useful app to make other tweaks and easily access device settings.
Note: SBSettings doesn’t add any icon on the home screen, you can access it by swiping the status bar (top bar) on your iPod touch.