Why does your phone's battery seem to last forever on some days, but gets sucked dry by noon on others? If it's an Android phone, it could be the apps you run — especially if they serve you ads — according to a new study.

Research from Microsoft and Purdue University, reported by ZDNet, looked at five of the most popular Android apps: Angry Birds, The New York Times reader, MapQuest, Free Chess and the Android browser. Using a custom-made app for the study called EProf, they tested the battery drain of each app on an HTC Passion running Android 2.3 "Gingerbread." EProf is capable of not only detecting how much power the app was using, but also the energy demands of specific app activities.

It turns out activities related to serving the user ads consume the most power. Of the total power consumed by Angry Birds, for example, a full 45% of it used to track ad-related user data (such as location). For Free Chess, the apps consumes between 65-75% on serving ads, uploading user info and tracking.

The New York Times fared better, with only about 15% of the energy drain attributed user tracking. As expected, the Android browser's power consumption varied depending on the sites visited, but the amount of power consumed to track the user averaged out to 16%.

Besides tracking, there are significant additional drains on the battery because of inefficient coding in ad modules. The research says that many ad-related functions create a "3G tail" — that is, a period where the ad is still using the phone's power-hungry 3G connection when it doesn't need to.

The paper says developers can make their apps more power efficient by bundling some separate functions into a single process. The research suggests that some apps could reduce power consumption by up to 65% with better-coded ad modules.

How do you keep your phone's power consumption to a minimum? Share your tips in the comments.

Image courtesy of iStockphoto, bizoo_n

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