Why is my battery draining on my iPhone 3Gs?

I just got an IPhone 3Gs that I ordered new on amazon. The phone came unlocked and Tmobile is my phone carrier. Before I even turned on the phone I let it charge to 100% and now that i started using it I've noticed that the battery is literally draining a percent or two every minute. I have blue tooth, 3G, and airplane mode turned off as well as the backlight turned down.

I have heard from a few different people the the iPhone 3G is one of the worst models when it comes to battery life, but they can't be as bad as one percent per minute.

So what I'm wondering is it because of the fact that my iPhone is unlocked that's causing the battery to drain so fast? I've done some research online and seen people complaining of the jailbroken apps such as Cydia making there phone die quickly. I checked and I don't have any of those apps.

So is anyone one else with an Unlocked iPhone 3Gs having the same problem and if so what can I do to fix this or improve the situation.

Turn Wi-Fi/ gps if it has it and check all your running programs.

MAYBE YOU HAVE A LOT OF PROGRAMS RUNNING IN THE BACKGROUND. IF YOU ARE IN HIGH SCHOOL (DON't KNOW HOW OLD YOU ARE) THE PHONE MIGHT BE CONSTANTLEY SEARCHING FOR SERVICE THAT KILL BATTERY FAST