Going to the home screen does not quit all apps. Also, you may want to look at your update settings for each app, you can turn off automatic searching.
Force Quitting To force an application to quit, Apple recommends that you bring the app you want to quit to the foreground. Then press and hold the sleep/wake button for several seconds, until the Slide to Power Off control appears. Release the sleep/wake button and hold down the Home button for another 7-10 seconds. Your screen will flash briefly and you will return to the main iOS 4 Springboard home page with its icons. This method works for all operating systems from iPhone OS 3 forward, and is the preferred method listed in the iOS 4 documentation.
Removing the Application from the Recents List There's actually a much simpler approach for quitting apps, and that's to use your recent app list. Double-click the home button to display the recently accessed applications. Press and hold any of the icons shown, then navigate to the application you want to quit and tap the red circled minus button. This sends a signal to the application in question that allows it to quit. The application will be re-added to the recents list the next time you launch it.
Also....
http://www.apple.com/batteries/iphone.html