Most of the android based mobiles are facing very crucial problem is battery backup ,By using this app you can extent the battery life.This free app makes it easy to manage the battery life on your device by providing various modes - each with its own setting for network, screen and battery usage to optimize battery life.
It also shows the remaining battery capacity in terms of talk time, web surfing, audio or video playback and can list functions that are consuming your device's battery life the most.
Battery monitor and JuiceDefender are the Cool apps for android ,Go to android market and search for JuiceDefender
https://market.android.com/details?id=com.latedroid.juicedefender&hl=en
https://market.android.com/details?id=com.latedroid.juicedefender&hl=en