iPhone 4S Repeatedly Dying Around 50% Battery?

So I've had my iPhone 4S since launch day just over two years ago and until a month or two ago I haven't had any significant trouble with it.

I'm finding that every day once there's around 50% battery life left on my phone, the device will abruptly die and shut off despite indicating that there's still plenty of battery life remaining. The phone will continue to show that there is no battery remaining for the next half hour or so, until I can finally turn it back on.

Once I can finally turn my phone on again, it will go back to saying there is about 50% battery remaining as before and then, after functioning normally for a few minutes, will suddenly die again. This cycle continues for the rest of the night until the battery is actually completely used and the phone dies completely.

As I mentioned above, this has been happening every day for the past month or so and it's beginning to be a huge hassle when I'm out late and I can't rely on my phone at all knowing it could die any minute and then remain unusable for the next half hour, if at all.

So I ask you, are there any troubleshooting tips I should try or will this warrant a trip to the Genius Bar?