Brand new iPhone 4s - battery barely lasts 3 hours of moderate to low usage?

I'm officially worried that something is wrong with this phone's battery.
Its usage statistics show that after 2 hours 31 minutes of usage and 2 days on standby, it has 38% battery left. I just turned used all the "fixes" offered online, such as turning off location servics and icloud, and yet the battery is still swiftly draining.

What can this be due to?
I saw an answer onlne that new phones' batteries haven't reached full potential, could this be it?
I've charged the phone twice already.
The thing is, the first time I charged it, I only charged it for about 4 hours. Could this have been too short a period of time? Should I let the phone charge overnight?
I don't know what to do here, I'm at a loss by now.

The iPhone has a lithium ion battery (more on that here ---> it's a video that debunks all the battery myths), and take your iPhone back to the store and ask about it… Seriously because i'm fairly certain your phone is messed up.

"Should I let the phone charge overnight? " Yes, that is why all Smart Phones instruct new users to do just that.

Calibrate iPhone Battery:

Use the iPhone until it it shuts OFF itself, due to Low Battery. Then Charge it back up without interruption, like unplugging it, to full charge 100%. Then before or after you do this, Reset iPhone, hold both home and power buttons until the iPhone restarts itself, ignore the "slide to power off slider", let the iPhone restart itself.

If you are constantly texting or talking on it then yeah that uses battery. It shouldn't drop much at all when not in use (mine doesn't) and I never shut it off.