Kindly accept our sincere apologies for the frustrated issue you're going through, but please make sure that the phone is updated to the last software update as the updates usually come to improve the device's performance. You should diagnose the battery from the settings > battery and device care > battery. However, the battery drainage depends usually on the apps you're using. Some apps may affect the phone's battery performance like the heavy games. Otherwise, you should go to the service center for further check.