The primary causes of a fast-draining phone battery are the:
1. On-time and brightness of display or screen
2. Amount of cellular communication, e.g., calls & data use
3. Graphics and video processing, e.g., games & face time/video calls
4. Background apps, e.g., location services, live wallpapers, widgets, & music apps
5. Cellular and Wi-Fi surveying/searching
6. Extreme heat or cold of the battery
7. Vibration alerts and haptic feedback modes
8. Secondary radios left on e.g., GPS, Bluetooth, & NFC