Something the man from Best Buy showed me was the "ultra power savings mode". When it's active, it cuts way down on power hungry things like the depth of the screen color pallette and I don't know what else. You can still email and text and take phone calls. According to that setting, you could go up to 15 days on a full charge. considering what the screen looked like, I'd say it was possible.
The S5 had the feature. It works very well on my S5. Incredible feature when you're in a pinch for battery life