Wonder why your iPhone's battery life is so short? The answer is right there on your phone. It's all those "free" apps!  But why do they cause such a drain?

Smartphone users wondering why their device’s battery life is so short should look at their free apps that researchers say are energy hogs. Computer scientists at Purdue University found up to 75% of the energy used by free versions of Android apps is spent serving up ads or tracking and uploading user data. When they developed software to analyze the energy usage of smartphone apps, researchers found only 10% to 30% of the energy use of popular apps such as “Angry Birds,” “Free Chess” and “NYTimes” went to powering the app’s core function. In “Angry Birds,” for example, only 20% is used to display and run the game, while 45% is consumed finding and uploading the user’s location using GPS coordinates so location-appropriate ads can be downloaded over the phone, the researchers said. That connection remains open for 10 seconds even after the data transmission has been complete, consuming another 28% of the app’s energy. Running just one such energy-hungry free app can drain a smartphone battery in around 90 minutes, the researchers said, mostly due to inefficiencies in the third-party code that developers use to generate profit from ads in “free” apps.