10 Advanced task killer is only useful for Android 2.x. Not necessary for ICS or JB. You have to turn off background/auto sync, GPS, and wifi if you don't use it, then it will save a lot of battery. Don't install those unnecessary apps, especially from Chinese companies. After I uninstalled a lot of unused Apps, my Samsung GS2 with Android 2.3 can run for upto 4 days with single charge(average 3-5 min voice and BT is always on because my car has BT).