How to Shut Apps to Save Battery Under iOS 4.2

The new iOS version 4.2.1 for iPad and iPhone brings with it multitasking. I could debate whether this is true multitasking or not (it's not) or whether Apple's model is sufficient for a mobile device where battery life is important (it is). But other blogs have done this pretty well already. So here I'm going to concentrate on one specific feature that is hidden but can change the way in which you manage your device battery life.

The following is true for the iPad and the iPhone, although the screenshots are fro the iPhone. (It's uploading them while I type this on the iPad - better than multitasking!)

When you open an app under iOS is stays open. This might not be a problem. A lot of apps just sit there and do absolutely nothing at all. That is nothing at all in terms of CPU activity. They do consume memory. But for battery life, we care about CPU and network activity. 

More often than not, an app will perform some background processing or download events from the Internet. Apple's multitasking model allows for apps to complete a download even if you close the app, or to connect to remote servers to poll for 'push ' notifications. If we're doing some work on the CPU or worse driving one of the several radios available on the device, then we are consuming battery.

So we need to close these apps - or at least the ones we're not using. To control the multitasking bar, you need to double-click the Home button. This gives you a multitasking bar at the bottom of your screen. You can swipe left and right to see the apps that are currently 'running' (or really I mean in memory). I swiped right until I found this view:

Great, so if I have been using my iOS device for a while since a reboot, it will have quite a list of apps. Most of which I don't need running. I don't want photos or Airfoil Speakers up and running until I actually want to use them.

Just like in the home screen, if I hold down on one of the icons the iOS switches to wobble mode.

In the Home screen, this signifies the ability to rearrange icons or to delete the app from the device. In the multitasking bar, this signifies the ability to close the app. If i click the minus button, I am not deleting the app from the device. (Yes, I was paranoid about this until I tried it too..) Rather I am closing the app completely and removing it from the iOS RAM and scheduler. That means it cannot receive background notifications and cannot consume battery - super! (Some apps still will, depending on their Settings configuration).

Once you have tidied up, you'll have a much neater application stack on your phone. Hopefully this should improve battery life too...

Remember you can restart any apps from the Home screen.