The hidden ways mobile sites and free games are killing your battery

You think you know how mobile browsing and games are killing your battery, but it's actually a bunch of unseen inefficiencies.

You know about some of the things that are putting such a hurt on your mobile battery that you can’t hit 4 p.m. without a warning. Streaming music over 3G, for example, or keeping the screen on for long camera sessions. But mobile web sites and certain free apps might be killing your phone’s juice in sneaky ways, according to some recent studies.

At the World Wide Web 2012 conference in Lyon, France, this week, Stanford researchers plan to present “Who Killed My Battery?: Analyzing Mobile Browser Energy Consumption” (PDF link), a study of how much power is consumed by mobile browsers on popular websites. They hooked up an Android phone and its battery to a rather geeky-looking monitor, and started surfing the mobile web. Even among those sites that offer mobile-optimized versions, there were some serious battery killers in the crowd: Wikipedia, Tumblr, IMDB, and Blogger, among others.

The main culprits are cascading style sheets (CSS) and JavaScript, which need to be downloaded and parsed by the mobile browser. On Wikipedia’s mobile site, the researchers actually modified the page scripts themselves, and came up with a version that reduced energy usage by around 30 percent, without any change to the content itself. Image formats (using JPG instead of GIF or PNG) make a difference, too, but the real difference is in how you handle interaction. The site that came out looking slim and powerful was Gmail’s mobile site, which uses HTML-based scripts to create an app-like experience, caches what information it can on the phone, and pares everything down for lower processing and data radio demands.

What would really help, the researchers suggest, was if more sites offloaded some of the computation, script-handling, and image scaling to their own servers, rather than asking your phone to handle it. Stanford researchers suggest both front-end proxies (which intercept data from web servers and render them in optimized form for the phone, as on Opera and Skyfire mobile browsers) and back-end servers (which the phone sends data to for processing). And if Google Analytics would allow mobile sites to be cached on the phone, instead of demanding fresh versions on every view for traffic-measuring purposes, that would help a lot, too.

Another, seemingly obvious but actually surprising mobile battery killer: free apps that monetize with advertising. You probably knew that playing Angry Birds put a hurt on your battery. But according to research by Purdue University and Microsoft, only 20 percent of Angry Birds’ battery consumption was for the mechanics and graphics of the game itself (which, if you think about it, are pretty simple sprites-hitting-other-sprites matters). 45 percent of the energy comes from keeping track of your location, so the free version can serve you targeted advertising. More energy draw comes from reaching out to ad servers to pull down those ads.

Yet another kill was the way in which apps leave connections open for up to 10 seconds after grabbing the information they need—a “3G tail,” as described in the Purdue/Microsoft study. Keeping that connection open to see if anything else new needs to drop in, like another pane for an animated ad, accounted for up to a quarter of Angry Birds’ energy consumption. To summate, at least 70 percent of the energy Angry Birds is pulling from your phone comes from advertising, location tracking for advertising, and connection demands for advertising.

In other words, games that cost no money can be very expensive in energy and hassle. And mobile sites are designed for mobile, but not really optimized. Let’s hope the people serving up content for our phones work to give us more battery life, so we can spend more time double-checking Jean-Claude Van Damme’s filmography and ensuring the property rights of aggrieved avians.

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