Help saving Battery Power

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http://androidforums.com – My phone lasts for a good amount of time, but I checked today and one of the apps that's using around 34% of battery is Facebook. Even though I use a task killer to stop it it re-opens in the background using up battery power (even when I'm signed out). Is there anyway to prevent apps from doing this w/o being rooted? If there are apps that can help feel free to let me know please. (General)