One of the reasons as to why Galaxy S3 battery drains during stand-by is because features like Bluetooth, mobile data, Wi-Fi may be on. It has been found that one of the biggest reasons for battery drain in Galaxy S3 is LTE. You can turn it off by going this way — Settings > More settings > Mobile networks > Network mode. The fact is that if you do not have LTE in your location, the phone battery will drain fast because it constantly searches for it.
Chrome enables tilt problem which could drain battery. You can start Chrome and then choose Settings > Developer tools and then uncheck Enable Tilt Scrolling.
Having Wi-Fi on Samsung Galaxy S3 turned on all the time can actually be helpful because it takes less power than connecting to a mobile network but in that case, you have to be in the range of WI-FI network or the battery will drain anyway.
The pre-installed apps on your Samsung Galaxy S3 can also drain battery life even if you are not using them. Many people have found that by disabling Samsung account and some Samsung apps, they have increased the battery life. In this case, go to Settings > Applications manager and choose the All tab then disable Samsung Account, Samsung Backup, Samsung Apps, Samsung Cloud Data Relay along with the stuff on the list that you do not actually use. The disabled apps move to the bottom of the All list so you can always re-enable them again if you face any problem.