Flip Battery Saver Power Up is a free app by Maxwell that allows you to save your phone's battery by up to 50%, simply by flipping it face down (which, via the app, deactivates the screen and turns on power-saving routines). It provides other functionality as well, such as cleaning up apps running in the background or tracking CO2 savings.
Flip and win
Flip Battery Saver Power Up uses your phone's motion sensor to know when it's flipped, face down, at which point the real savings start. Thus, an older phone might struggle to detect when the app is trying to do its work, but this shouldn't happen often. Otherwise, the app tracks how much power has been saved by the app in terms of CO2 (it really is efficient!) and can also clean up your phone's memory.
Basically, Flip Battery Saver Power Up extends your phone's existing capabilities. Though you can mimic its battery-saving capabilities by turning your phone's screen off, flipping your phone over is easier to both start and stop, and Flip Battery Saver still does a little more than pressing the button on the side of your phone can. If you're environmentally conscious or just want a bit more zip out of your battery, Flip Battery Save Power Up really will power things up.