I've a peculiar problem in GSM only mode. I'am using only one sim. whenever I put it in GSM only mode, after one or two hours if kept idle, the phone gets heated. If I unlock the phone, battery quickly drains 10-15% within 2 mins then goes well. again after half an hour or so this repeats if kept in idle. This way within 5 to 6 hours battery drains almost 40 to 50%. Moreover from battery usage stats this sudden drop in battery percentage could not be explained as those 40 % charge remains unaccounted. this problem never occurs in WCDMA only mode or in flight mode.

Enable Power Saving Mode:

1. Tap “Apps” on the home screen
2. Go to “Settings”
3. Swipe to “System” and tap “Battery”
4. Tap “Power saving mode” to set the slider “ON”
5. Adjust the battery percentage at which Power Saving Mode enables automatically

Enable Ultra Power Saving Mode:

1. Open the apps drawer
2. Access “Settings”
3. Under “System”, tap “Battery”
4. Tap the “Ultra power saving mode” switch and set it to “ON”
5. Tap “Agree” in the terms and conditions pop-up
6. After the mode activates, you can tap “+” to add more applications to the home screen

Lower the Screen Brightness and Timeout Duration:

1. Tap “Apps” on the home screen
2. Access “Settings”
3. Under “Device”, tap “Display”
4. Tap “Screen timeout” and select a lower value, like “15 seconds”
5. Disable “Automatic brightness” if necessary, and drag the brightness slider towards the left to decrease luminosity

Disable Background Data:

1. Go to the phone’s “Settings” menu
2. Under “Connections”, tap “Data usage”
3. Tap “More” > “Restrict background data”
4. Tap “OK”

Disable Wi-Fi, Hotspot, GPS, and Bluetooth:

1. Open the apps drawer and access “Settings”
2. Under “Connections”, tap “Tethering & Mobile hotspot”
3. Disable the Hotspot switch and return to the home screen
4. Swipe the “Status” bar down
5. Tap the “Wi-Fi”, “Location” and “Bluetooth” tiles to disable these features

Switch from 4G to 2G:

1. Go to “Settings”
2. Under “Connections”, tap “More connection settings”
3. Tap “Mobile networks” > “Network mode”
4. Select “GSM only” to switch to 2G

Change App Sync Settings:

NOTE: You can improve battery life in the long run by setting your accounts to sync less data / less often.

1. Access “Settings”
2. Scroll to “Personal”
3. Tap “Accounts” and select the desired account
4. Clear the boxes associated with the sync options you want to disable
5. When done selecting / deselecting check boxes, tap “Menu” > “Sync now”

Minimize the Use of Third Party Apps:

NOTE: Some of your third party apps can affect your phone’s battery life even when you don’t use them, simply because some apps perform regular processes in the background. Thus you could improve battery life by disabling or removing third party apps you don’t use.

1. Go to “Settings”
2. Scroll to “Device”
3. Tap “Applications” > “Application manager”
4. Swipe to the “Downloaded” screen
5. Tap the desired app and tap “Disable” / “Force stop”
6. To remove an app completely, tap “Uninstall” twice to confirm

Keep Your Phone Updated:

NOTE: Certain software updates can include improvements to battery life, so you should keep your phone up to date. To check for new updates:

1. Swipe to “System” from the “Settings” menu
2. Tap “About device”
3. Tap “System updates”
4. Assuming that a new software version is available, follow the on-screen prompts to apply it (you may have to reboot your phone during the process)