there is no power saving mode on the menu you specified on my samsung galaxy ace 3. I have lock screen, display, sound, home screen mode, call, blocking mode, safety assistance, accessibility, language and input, motions and gestures, smart screen.
What now?

Enabling Battery Saving Mode:

1. Press the "Menu" button while viewing a home screen
2. Tap "Settings"
3. Access the "My device" tab
4. Tap the "On / Off" switch next to "Power saving mode" and set it to ON (green color)
5. Tap "Power saving mode" and customize the way the feature works, by clearing or marking the check boxes next to "CPU power saving", "Screen power saving" etc.

Changing the Wallpaper:

NOTE: if you intend on maximizing battery life, it's highly recommended that you don't use a live wallpaper. To switch to a normal wallpaper:

1. From any home screen, press "Menu"
2. Tap "Set wallpaper" > "Home screen"
3. Select "Gallery" or "Wallpaper"
4. Browse through your gallery, select the desired image, set / drag / resize it and tap "Done". If picking an image from "Wallpapers", select the desired one and tap "Set wallpaper" (no cropping needed)

Adjusting the Screen Brightness and Timeout Duration:

1. While on the home screen, press "Menu"
2. Tap "Settings" and go to the "My device" tab
3. Tap "Display" > "Brightness"
4. Clear the check box next to "Automatic brightness"
5. Drag the brightness slider to the left, and set it to a lower but visible level
6. Tap "OK" and access "Screen timeout"
7. Select a lower timeout duration, such as "15 seconds"

Disabling Bluetooth, GPS, Wi-Fi and Portable Wi-Fi Hotspot:

NOTE: a smartphone's connectivity features require a lot of battery, and it's highly advised that you disable all of these features when not in use.

1. While on a home screen, press "Menu"
2. Tap "Settings" and tap the "Connections" tab
3. Press "More networks" > "Tethering & Mobile HotSpot"
4. Tap the switch next to "Mobile Hotspot" and set it to OFF (grey color)
5. Go back to the home screen and swipe the "Status" bar down
6. Tap the "Wi-Fi", "Bluetooth" and "GPS" icons to disable these features

Changing the Sync Settings for Apps:

1. Press the "Menu" button while on the home screen
2. Tap "Settings" and go to the "Accounts" tab
3. Under "My accounts", select the desired account type, such as "Google"
4. Tap the available sync settings to adjust them
5. Tap your "user name" or "email address" at the top of the display to adjust additional sync settings
6. You can tap each applicable category and mark / clear check boxes to enable / disable sync

Disabling Background Data:

1. Press the "Menu" button while viewing a home screen
2. Tap "Settings" and access the "Connections" tab
3. Tap "Data usage" and press the "Menu" key
4. Mark the check box next to "Restrict background data"

Minimizing Usage of Third Party Apps:

1. From the home screen, press "Menu" and tap "Settings"
2. Access the "More" tab
3. Tap "Application manager" and go to the "Downloaded" screen
4. Select an application ad tap "Disable" to turn it off
5. To completely remove an app, tap "Uninstall" > "OK"

Switching from 4G to 2G Connectivity:

1. Access the phone's settings screen by pressing "Menu" on the home screen
2. Open the "Connections" tab
3. Tap "More networks" > "Mobile networks" > "Network mode"
4. Tap "GSM only" in order to switch to 2G only
5. To return to 4G, tap either "LTE / GSM / WCDMA (auto connect), or "GSM / WCMA (auto connect)"

Updating to the Latest Software:

NOTE: The steps below will give positive results only if Samsung has released a new update for your phone that fixes or improve battery life. Otherwise, if no new software update is available, your phone's battery performance will not change.

1. From the home screen, press "Menu"
2. Tap "Settings" and access the "More" tab
3. Tap "About device" > "Software update"
4. Follow the on-screen prompts if an update is available, in order to apply it