handset running full-power even when the app is loaded. For example, with Angry Birds, 45% of the power used to run the app is for the third-party Flurry ad network. Of that 45%, 15% is used by the GPS on your phone to confirm your location and 24% belonged to the 3G "tail".
An Android user can use a lot of energy just opening a search page in the native browser. The GPS and 3G requirements for such an act would add up to 16% and 31% respectively of the total 2,000uAh of battery life burned. Do you ever browse CNN on your mobile device? That will cost you 2,400uAh in power, mostly for data as there is no need to find your location.
To show you how much energy is used after an app loads, a sample app was devised by the guys behind the study and connected with a remote server. 5 packets of data was sent which used 127uAh of energy. After the app loaded, it ran for another 6 seconds, burning 187uAh in energy for a total of 57% of the energy used. That "tail" also happened to occur if the routine was delayed by 5 seconds after the connection was made. This extra use of energy also shows up when a bug called a "wakelock" tricks the device into running at a high-power state and keeps it running at that level. The study found that such bugs were in Android's Mail program and the Facebook app.
Despite the theory that ad servers were responsible for the vast majority of energy use to run a free app, that most of the energy used to run applications are used for I/O operations. The conclusion of the study was that further research is needed to optimize the use of battery life when running Android apps.