Apps running in background

[andy wright]

My iPhone 3GS running with ios4 loses its battery life quickly and I was wondering if it is because I have unwanted apps running in the background. How can I tell which apps are still running in the background?
Andy

 

[Lingham]

Double press the home button

 

[andy wright]

I have tried that but I thought all that did was to put the apps in order of last usage. I have 50 plus. Surely these aren't all running in the background.
Andy

 

[Fuchal]

I have tried that but I thought all that did was to put the apps in order of last usage. I have 50 plus. Surely these aren't all running in the background.
Andy

You're right, you can't quickly tell which apps actually have processes open in the background. But you can do some quick logic - the main offenders are usually VoIP or GPS apps. If you have Skype in that list, kill it.