apps like contacts, call history, texts, etc. will NOT kill your battery and you don't have to keep killing apps everytime you open one.
1. The OS will kill apps, automatically, when it needs to. (whever memory or performance begins to suffer)
2. If it bothers you, you can exit out of apps and they will not show in the task manager as "running". Except for built in apps like camera, IE, etc.. but there is no need to kill these apps after every use. (See number 1.)
3. If you are experiencing poor battery life and you have a mol3 updated Q and good network signal (3bars or better in EV area), then you are obviously a heavy user and should upgrade to an extended battery.
Hope this helps.
