IDG Answers is a community of experts who are passionate about technology. Ask a question or answer one below.
I saw an article about this on BBC that discussed a Purdue University study of Android and Windows Mobile smartphone battery use. Apparently up to 75% of a free apps battery consumption was devoted to powering advertisements. One specific app they looked at was Angry Birds, where they found that only 20% of the total power use was from playing the game. 45% was used to find your location for use in targeting advertising. One thing that was interesting to me was that apps used a 3G connection to download advertising and then left the connection open for up to 10 seconds after the task was complete. That 10 second "3G tail" repeated over the time the game was played was responsible for about 25% of the total battery use of the app. http://www.bbc.co.uk/news/technology-17431109
It's a choice you have to make. Pay for an app and get better battery life, which is a big issue, particularly for many Android users, or get it free and pay for it through increased energy consumption. Developers could probably minimize the excess battery use, but they really don't have much of an incentive to do so.