Please follow below steps may improve battery backup:
1. Enable “Power saver” (Settings > Power management)
2. Close apps that are not used (Bluetooth, WiFi, GPS, etc.)
3. Adjust sleep time and brightness (Settings > Display)
4. Boost memory when you see memory consumption is high with no app running,
5. check for background running applications, stop/disable unwanted apps, you can manage apps from auto-start manager.
To recalibrate battery, charge your phone to 100% without interruption.
then discharge it normally till 0%(phone gets switched off).
charge it to 100% in switched off condition and keep it in that state for a little more time.
now switch on your phone in charged condition and unplug when ASUS logo appears.
keep the phone unused for 5 mins.
you will get far better battery life as the battery stats.bin file will be updated.