ABCNews

By Jim Avila and Tia Brueggeman

Ever wonder why your smartphone battery runs out so quickly?

A new study by Purdue University has the shocking answer. It's the Apps, popular applications that are using more energy when they are supposedly idle than when active. University researchers say on Angry Birds and Facebook 65 percent to 75 percent of the energy used is spent on sending your information to advertisers.

In fact, "Of the total energy consumed in the Angry Birds game, only 20 percent of energy is used on the game itself," said Y. Charlie Hu, Purdue University professor at the School of Electrical and Computer Engineering and the head of the study. "The remaining 80 percent is spent on the advertisement module.

"The free version (of an application) is not free, there's a hidden cost," Hu said. "That cost is the battery life on your phone."

Hu and his team of researchers developed eprof, a sophisticated tool that measures energy usage in applications. According to the study, "when a user plays a single game over 3g, the app spawns 35 threads." These threads communicate with third parties generating ads and transmitting data about the user.

"Our motivation is straightforward; a lot of people find this energy drain problem. It's a fundamental problem of Smartphone users," Hu said. "We went online and saw where thousands of smart phone users complained about battery drain."

With this in mind, Hu and researchers tested 21 of the most popular applications. Of the five highlighted in the study, three or four appeared on the list of the top 10 most popular android applications, including Angry Birds.

Hu said there is more research to be done.

"This study is part of a bigger project, raising issues of these 'energy bugs,'" Hu said. "Unlike a computer, instead of causing the application to crash, it's making the application consume more energy than expected."