The screen is too bright
One way that your battery runs out of battery is when your screen is too bright. The brightness will affect not only the battery but also your eyes. It's better to set your phone to automatically adjust to the lighting of the ambiance. You can also reduce the time it takes for your phone to go off whenever you stop using it.
You forget to switch off your WiFi
You are using your phone WiFi where it's actually functioning. After leaving the place, you forget to switch it off. If it keeps searching and alerting you whenever WiFi is available, your battery will run out pretty fast.
You receive notifications every second
Why won't your phone battery drain when your phone keeps alerting you of Instagram, Twitter, Facebook and other notifications? Then you don't need to complain. You check your browser for notifications rather than using the apps. You can also turn off notifications
Background apps are running
You should check the background apps draining your battery so that you can 'kill' them. Your phone may alert about the apps consuming the most battery. But sometimes you have to disable these apps yourself by refreshing or cleaning your phone.
Your battery is bad or damaged
If you have tried all of the aforementioned reasons and your battery still runs out very fast, you should consider replacing the battery because it may be bad or damaged.