The 5800 is an S60 smartphone, and can run several applications at once (for example you can listen to music while surfing the web and receiving instant messages). However, the more applications you run at once, the quicker the battery will be drained, so it’s a good idea to shut down any applications you don’t need.
How to shut down running apps in Nokia 5800 XpressMusic phone.
You can see all the current running applications by doing the following. Hold down the white menu button for a few seconds (you can let go of the button once the Open Applications menu appears). Select an icon in the Open Apps menu to go to that application, and exit the app from its own options menu to shut it down.
This might be easy method, most apps can be shut down by going to them and pressing the red button below the screen. The fewer apps that run simultaneously, the longer the battery will last. Running fewer apps simultaneously will also make the phone run faster overall, because it has less to do at once.