Decreasing the screen timeout along with lowering the display brightness help you get more battery life while using your Amazon's Kindle Fire. To automatically turn of the screen after a specific idle time on Kindle Fire, do as follows:
1. Drag down the notification panel and go to Settings.
2. Tap on Display & Sounds to enter the settings
3. Tap Display Sleep and select one of the available options: 30 seconds, 1 minute,....,1 hour, or Never*
* The Never option keeps the screen On as long as there is battery power.