What I would first do would be to turn on “Low Power Mode” in the battery menu of the Settings. Low power mode temporarily reduces power consumption by minimizing the iPhone’s activity of fetching mail, certain Siri functions such as “Hey Siri”, background app refresh, automatic downloads, certain visual effects, etc,. So really you can say that this mode puts the iPhone into state of hibernation for its features. This helps the performance of the battery since the phone won’t constantly be uploading and downloading information.
If you also use your iPhone for work and on the go make sure to turn on “Night Shift” at night time to help reduce the displays backlight usage. Also close out any applications that you may not need running in “App Switcher” when you are done. This helps reduce the iPhone from having to throttle CPU speeds which burn the battery up quicker.
The biggest one I tell people, is to please, please, please turn on Auto-Lock. this feature locks the iPhone after about 30 seconds - 1 minute after inactivity.
All these tips and tricks really will help to conserve your iPhone’s battery and help the battery last longer without replacement. You should notice that the iPhone will hold somewhat of a better charge than before, but you will also notice that some features (if used) will have to be access or set manually rather than the phone doing them for you.
Hope this helps you good luck!