Why is my battery time so much shorter after jailbreak?
I can see two main possibilities: 


Apps like FolderCloser, NoLockScreen, and SBSettings shorten battery life by requiring heavy background processes. The only solution to this would be either to not install these apps or restore the phone to its original state altogether (and not have these apps installed). I am convinced that jailbreaking allows for processes that are not in phase with Apple's careful thriftiness of battery use.
Your battery is not calibrated properly so your iPhone miscalculates the remaining percentage. The solution here would be to drain your battery completely and then fully charge it.


Good luck! And know that you can restore the phone to its original state.