We love the rich colors offered by the S4's large 5-inch display, but it can be a power hog. Take control by going to the Display section under the My Device tab. We’d start with enabling automatic brightness, which makes your screen only as bright as it needs to by responding to ambient light. (You can also toggle Auto brightness by swiping down from the top of the screen.)
Also, consider setting your screen mode to standard to keep your screen’s color, contrast and other levels the same at all times. Finally, you should find a darker wallpaper and lock screen image. Generally speaking, AMOLED displays use less power to brighten dark pixels than brightly-colored ones.
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