The next one (no jailbroken) doesn't really give you an actual percentage, but its pretty cool, it TELLS you the percentage.
Go into general settings>accessibility>voice over and turn it on. then, go back to accessibility and go down to where it says "triple click home" this option configures how the home button behaves when you triple click it. Check the option that says "toggle voice over". Now exit settings and triple click the home button to activate voice over and hit the battery icon at the top right. The weird female robot voice should read you the actual percentage of your battery.