Question

How can I make my Samsung S3 last for more than three days on the battery?

Answer 1

Try to use as less as possible the hungry apps such as chatting apps

If possible, limit your Wifi habitude or internet traffic

If nothing works, try to add an extternal battery, whenever you smarphone is reaching the end of battery. Samsung developed good batteries, I use one for my Xperia unit

Answer 2

by adding an external battery case which will allow you to have more fun with your smartphone.