Why is my iPhone battery draining so low?

So I bought an iPhone 4 two weeks ago and for a week the battery was GREAT. But now everytime I use it for something the battery drains super fast. Only when it's on standby is it still good, any tips?

Did you update it? My battery drains faster too, and I think one of the updates said something like "reduced battery charge" or close to that.

One of the reasons why that's happening is probably because you have way too many app running at the same time.