It affects battery life yes, but not that much unless you always have it at 100%. You can use auto brightness even if you want it a bit darker. iOS will learn what brightness you prefer at different lighting conditions and adjust to that.

Does brightness drain the battery?

In an hourlong test, an iPhone 6S used 54% less battery power with the screen brightness at minimum as compared with maximum brightness. An Android test phone used 30% less. ... The Wirecutter found that enabling auto-brightness saved a good amount of battery life.

Does brightness affect battery percentage?

Use auto-brightness for the screen

In an hourlong test, an iPhone 6S used 54% less battery power with the screen brightness at minimum as compared with maximum brightness. An Android test phone used 30% less.