Was the phone new or refurbished/second hand?
I suppose the first place to start looking is in settings and battery to see what's using the battery so much.
Are all the apps you have updated. Playstore and Galaxy Store?
Have you tried Wiping the Partition Cashe on the phone?
Turn off your phone.
Connect your phone with a USB cable
To PC or another Samsung mobile
You will see the charging icon on your screen.
Wait till it shows charging with battery percentage.
Next, press and hold the Volume up and Side key simultaneously.
You can press the volume up button just before the Side key.
The Samsung Logo followed by
Samsung Galaxy appears on the Screen.
At this point, release the keys
Phone will boot into Android Recovery mode
In Android recovery mode, using Volume keys, choose “Wipe Cache Partition” .
Use the power button to accept that.
You will then see its cleared.
Then the top option, reboot phone.
Press the power button to reboot the phone and then sign in normally
