There are several possible reason for rapid battery drain on smart phone:
1. If a base is station miles away from the phone (Signal strength bar is low), the phone uses greater power to send &
receive registered information and as such consumes more power, thus draining the power of the battery.
2. The battery is depleted quickly by turning on LCD Back Light.
3. If applications are not closed correctly, pressing the home key, they run in the back ground and drain the battery.
4. Rooting authorizes Super User within Android system range sphere, which may cause data change in battery management
sphere, accelerating battery rundown.
5. Applications requiring regular data updates such as stock/weather widgets are likely to accelerate battery drain if the
update cycle is set to short.
6. Real-time synchronization, consumes power quickly e.g. real-time email checks or contact synchronization.
7. Most of the widgets installed on the home screen cause battery drain.
8. Live wallpaper consumes more power than normal wallpaper, thus causing rapid battery drain.
9. Smart phones automatically detects Wi-Fi wireless router or Wi-Fi zone, when the Wi-Fi is turned on, and as such drain
10. When Bluetooth is turned on, it searches for other Bluetooth devices, and as such consumes power and drains the battery.