Battery life has long been a major complaint for most HTC EVO users since the original EVO was first released in June 2010. But according to a new study from Purdue University, free ad-supported apps might be the biggest culprits in keeping your battery from lasting the entire day.

According to Abhinav Pathak, popular apps such as Angry Birds, Free Chess, and the New York Times only use about 10-30% of their spent energy to power the app's main function. The other 70-90% of energy is spent delivering ads.

For example, the free ad-supported version of Angry Birds only uses about 20% of its energy to run and display the game. 45% is used to find and upload the user's GPS location to subsequently download location-based ads over 3G. Additionally, the 3G connection then stays open for about ten seconds, even after data transmission is complete – this consumes another 28% of the app's energy.

According to the study, the only way to fix this is for app developers to code their front and back end better. Of course, users could always uninstall ad-supported apps, or opt to purchase the paid, ad-free versions, but that is a less-than-ideal solution.

So next time your battery is low, just try to put down Angry Birds until you find a power outlet.

[New Scientist via Phandroid]