IPhone 4S too hot & battery depletion?

I have had my iPhone 4S for just under a year and are having serious issues with it which weren't so bad earlier in the year. I realised since I've had the phone that the battery wasn't long-lasting but it has gotten much worse.

Over the past 3 days I have gotten the Temperature lock-out mode come into action and prevent me from using my phone for some time (this happens on idle or under minimal stress.)

Also, my battery lasts under 4 hours from a 100% charge.

What's wrong with my phone and what are my options?

Added (1). As I'm currently not at school due to the Christmas break, no music has been played on my phone for some time as I'm usually with my friends, at my computer or in my car. I never use my mobile for navigation purposes. I've actually used my phone lesser than usual, so I'm stuck!

If your battery drain is caused simply by use -- you're running background music or navigation like a fiend, for example, your only choice is to get a few more charging cables or battery extenders. If, however, you're doing roughly the same things you've always done and getting substantially less battery life for your troubles, there's a chance a few troubleshooting steps might just help get your power problems back under control.

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