Update: The higher “computed power use” for WiFi has been confirmed to be an algorithmic error on Marshmallow. So WiFi isn’t draining battery. The solution below works to fix the wrong reporting.

WiFi draining battery on your Android device running the freshest release of Android (Marshmallow)? You’re not alone. +Nomaan Mohammad over at Google+ found the
“computed power use” (new feature on Marshmallow) for WiFi higher than anything else on his device, which certainly tells that WiFi is taking the most of battery power.

However, Nomaan also mentions that this was probably wrong reporting by the OS than a real battery drain by WiFi. The stats reported WiFi using more battery power than Screen, which is almost unreal.

Anyway, if you’re seeing the issue on your device as well, below is a fix for this:

Note: Before you proceed, backup your WiFi passwords and other network settings through Google’s backup service.

  1. Go to Settings > Location > open Menu (three dots, top-right corner) > select Scanning > Turn Off WiFi scanning.
  2. Go back to Settings > Backup and reset > Network settings reset > tap “Reset settings”.
  3. Reboot your device.

via Google+