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It could be a rogue app that is draining your battery in the background, did you look at your battery status to see what is using up the battery?
Are you connected to WiFi most of the time or just the regular cell connection? Having poor or weak cell reception can cause a high battery drain and would not show up in the battery status.
You could also try putting apps that you do not use often to sleep, go to Settings > Device care < Battery (touch the hamburger menu the 3 dots in the upper-right) > Settings > Sleeping apps. Put all your apps in there (except the ones you know will need to run in the background, such as text messages or music apps that need to run when the device is idle). Otherwise, some apps will run unrestricted and drain the battery when your phone is sleeping.
If that does not work you can try clearing the phone cache partition.
If the battery drain is still there then I would suggest a factory reset.
If everything else fails you can do an exchange as long as you are within your 15-day satisfaction guarantee.
To learn more about that see here.