Battery Boost is a simple app giving recommendations on how one can use the iPhone / iTouch to the optimum by conserving the battery in right areas.
Increase your battery life with an increase in game play, increase in video playback, increase in audio playback, increase in talk time and increase in net browsing time. There are few tips even I was not aware of. Would recommend trying the free app rather than buying it.
Note: The app suggests updating to the latest software versions, but you better know – what that does to your jailbreak 😛