Everybody knows that playing games on your smartphone is a death sentence to your phone’s battery. When I first succumbed to my light addiction to Words With Friends, I actually had to start taking my battery charger to work with me because my iPhone wasn’t making it through a whole eight-hour shift (although actually working at work would probably have also preserved my battery, too, but that’s neither here nor there).

If you’re like me, you assumed that the battery-suckage was due to the power required to actually run the game. While your phone’s battery does diminish when you play the game (of course using your phone will use up your battery), it’s not running the game that’s killing it – it’s the fact that you’re using free apps.

As you know, or at least have noticed, free apps are always accompanied by the display of ads. The ads are, after all, how the apps pay for themselves and why you’re permitted to download and enjoy it for free in the first place. However, a new study by a research team at Purdue University has found that the energy used to produce those ads can account for as much as three-fourths of the total energy used to run the apps.

If you are curious enough to check out the research paper, one question that will likely arise before you even get out of the first paragraph of the abstract is: why didn’t the researchers include iPhones in the study? It wasn’t an oversight by any means on the researchers behalf but, rather, Apple’s infamous garden wall.

Abhinav Pathak, the lead researcher for the study, took a minute to reply to an email I sent him in which I asked about, among other things, the omission of iOS devices from the study. “The theoretical framework behind EProf [EProf was the diagnostic tool developed by Pathak and his team for the purpose of this study so they could assess the energy consumption of apps] is Operating System independent and we have implemented the tool for 2 OSes (Android and Windows Mobile 6.5) to show that it actually works across OSes,” he said. “However building the tool requires OS level changes to perform event logging. We do not have access to iOS to implement our lower level changes. Hence we did not port EProf to iOS and hence no app energy measurements from iPhone.”

One app that got a lot of attention from the researchers, and one I’m sure you’ve noticed puts an absolute beating on your battery, was Angry Birds. It’s almost impossible to get more than a couple of hours of untethered playtime before you have to leash yourself to a power outlet to continue to feed your need to play. As it turns out, only 20% of the energy used to power the app is used on actually running the game. 45% of the energy used is on your phone’s GPS and locating you in order to deliver locale-specific ads over your 3G connection.

The study opens up a promising exploration into smartphone energy consumption and, hopefully, developing ways in which that energy can be conserved as newer apps are developed. If you think about it, it makes total sense that there should be some sort of energy regulation on battery usage within smartphones, especially since so many of us have interwoven the device into our daily lives. Pathak believes that the energy drain from app-producing free apps can be cut by developers through some clever programming.

“So far, app developers did not have any tool which could give them in-depth energy consumption details about their app and hence were completely oblivious to the energy drain inside the app,” Pathak said. Now that the researcher’s energy analysis tool EProf has shown that these apps are draining the battery, Pathak added, developers should now be able to address the problem with excessive battery drainage due to ads generated by free apps.

Pathak also mentioned that there is a forthcoming paper that hopes to address the solutions of some of the “most notorious app energy bugs.”

In the meantime, it might be in your best interest to pay for the full version of Angry Birds Space later this month so you’re not constantly hugging a wall outlet just to destroy some green pig forts.