Nokia Lumia 521 - How can I prolong the battery life of my Lumia phone?

Save power automatically by tapping Settings > battery saver. When Battery Saver is on, a small heart icon appears over the battery icon, and your phone does not automatically receive mail and calendar updates, update some live tiles, or allow apps to run in the background. 

You can also try the following:

Turn off services and functions that you do not use: 

  1. Switch off location services: Tap Settings > Location services > Off.
  2. Switch off NFC: Tap Settings > tap+send, and switch NFC sharing to Off.
  3. Switch Bluetooth off: Tap Settings > Bluetooth, and switch Status to Off.
  4. Stop your phone connecting to games: Tap Settings, swipe to applications, tap games, and switch all relevant settings off. 
  5. Check which apps are running background tasks and block the ones you do not need:  On the start screen, swipe left, tap Settings, swipe to applications, and tap background tasks. Tap the app you want to block, and tap block.
  6. Switch off the Xbox Music cloud collection feature in Windows Phone 8: Tap Settings, swipe to applications, tap Music+Videos, and switch settings to Off.
  7. Close apps you are not using: Exit from the app by pressing the back key.

Change the frequency of certain events:

  1. Change your mail settings to retrieve mail items less frequently: On the start screen, open the mail account you want to modify, tap ... > Settings > sync settings and change the setting for Download new content.
  2. Set your phone screen to switch off after a shorter time: Tap Settings > lock screen (Lock+wallpaper), and change the setting for Screen times out after.
  3. Stop your phone scanning for Wi-Fi networks: Tap Settings > WiFi (> advanced), and uncheck the Notify me when new networks are found check box.

Other tips:

  1. Reduce screen brightness: Tap Settings > brightness, switch Automatically adjust to Off, and switch Level to low.
  2. Change the setting for Nokia Glance Screen in Windows Phone 8: Tap Settings >glance, and switch Glance Screen to peek. To save power switch Glance Screen to Off.
  3. Use double-tap to wake up your phone only when needed: Tap Settings > touch, and switch Double tap to wake up phone to Off.
  4. Use a Wi-Fi connection to the internet or set your phone to use 2G (GSM) network only: Tap Settings > mobile network (or cellular) > Highest connection speed.
  5. Always charge the battery fully: Tap Settings > battery saver > battery information.
  6. Use wired headphones, rather than the loudspeaker.
  7. Check that your apps are up-to-date: Go to Store. If there are updates available, tap Updates to update the apps.

If the battery keeps draining fast:

  1. Restart your phone by pressing and holding the Power and Volume Down keys simultaneously until the phone vibrates. Release and the phone will restart.
  2. Out of date or invalid passwords for email and social media accounts affect battery life. Delete and re-create your account profiles by long tapping the relevant account profile in (Settings > email+accounts). If this fails, switch your phone to flight mode and reboot. Then delete your email profile, turn off flight mode and re-create your email. Apply this for all stalled account profiles (Mail Account which is set as Microsoft Account on the device cannot be removed manually).
  3. The battery may be wearing out and require replacing.