Smartphone Battery Drains A Lot Even With Dark Screen

Background app updates, cell tower pings and other hidden activity accounts for almost half the battery drain on Android phones. Christopher Intagliata reports.

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down to 10 percent? Time to turn down the brightness on the screen, right? It's a classic strategy to squeeze more . And it works. But that trick might be less effective than you think. Because it turns out nearly the battery drain on a phone happens when the screen's not even So says a study presented at , in Portland, Oregon. [Xiaomeng Chen et al, ]

Researchers eavesdropped on the activity of more than 1500 Android phones—specifically, the Samsung Galaxy S3 and S4. They used an app they developed called . The app logs the energy drain of the phone's apps and activities as they happen. (And you can try out eStar Energy Saver yourself, if you have an Android.)

They found that some of the battery drain happened while the screen was off. A lot of that energy suck was apps updating in the background—downloading headlines and weather, while you're not actively using them. And different of the same app require different energy supplies. For instance, some versions of the Facebook app were twice as energy thirsty as versions. So app version choice could slow your battery drain.

But one of the most hidden energy draws, zapping 12 percent of the battery, was just cellular paging: the pings from a cell tower every 1.28 seconds, that tell your phone if a call or message is on the way. Which is, ultimately, the price of being connected.

—Christopher Intagliata