Battery saver mode, or your battery may just be old. Batteries get worse over time. They lose charge capacity, or at least Li-ion ones do. So depending on where you are with your battery, that will decide what you need to do. Keep in mind battery saver mode kills performance. Another thing to note is that this laptop isn't meant to be used on battery especially for gaming. Just think about what is being asked of the laptop boasting a GTX980M inside it and you want to "extend" battery life? Doesn't work like that unfortunately for all of us lol.
When you use it off Power, are you gaming? Or you just want more battery life for simple tasks? Don't expect more than an hour with gaming and running on battery. It's just not what this laptop was designed for. These are power hungry machines and if you want battery life, maybe buy a new laptop with a lower model GPU and put it on Balanced mode for power settings and just don't play any crazy games. OR stop trying to game for extended periods of time with a gaming laptop on battery. Mine is at my desk and it's always plugged in. Plus I have a triple monitor set up so I seldom take my laptop anywhere else in the house. I only move it if i'm going to a friends house or something.