Although the little battery icon in the upper right corner of the iPod’s screen is cute, it provides only a very general idea of the iPod’s remaining battery charge. It is possible, however, to tell iPod that the battery voltage should be displayed instead.
To force the iPod to do this, create a file called _show_voltage inside the Device folder located under the iPod_Control folder. Just attach the iPod to your Mac and make sure it is mounted as a removable hard drive before running the following command:
touch /Volumes/My iPod/iPod_Control/Device/_show_voltage
Removing that file will make iPod battery charge get displayed as the little battery icon.