'Free' phone apps come with energy cost WEST LAFAYETTE, Ind., March 19 (UPI) -- Smartphone users wondering why their device's battery life is so short should look at their free apps that U.S. researchers say are energy hogs. Computer scientists at Purdue University found up to 75 percent of the energy used by free versions of Android apps is spent serving up ads or tracking and uploading user data, NewScientist.com reported Sunday. When they developed software to analyze the energy usage of smartphone apps, researchers found only 10 to 30 percent 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 percent is used to display and run the game, while 45 percent is consumed finding and uploading the user's location using Global Positioning System 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 percent of the app's energy, they said. 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.