For those times when a simple percentage isn't enough.
This unlocks the hidden battery usage menu Apple uses internally during development (found in Settings->General->Usage->Battery Usage). It contains much more detail than the standard menu, check the screenshots for an example.
At the bottom there's an option to show/hide daemons from the list. The "Save For Demo" button generates a plist representation of the data and stores in "/var/mobile/Library/Logs/BatteryUIDemos"
You can download DetailedBatteryUsage from the Big Boss Cydia Repository. If you haven't jailbroken yet, use the iClarified Jailbreak Wizard to do so.