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I woke this morning and discovered that my phone's battery was at 70% capacity, even though it had been fully charged when I went to sleep. I went into the battery settings, and found that Android System is primarily responsible, having kept my phone awake the entire time. I searched a bit, and this does not appear to be normal behaviour. Reception and wifi are fine, and power saving is on. I'm hoping that there is an explanation and solution to this.

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"Android System" can mean multiple things. I'd suggest you install BetterBatteryStats and check who's really responsible for "Wake Locks". You can find the app in the Playstore and at the XDAs. –  Izzy Oct 11 '12 at 16:33
    
So this is a actually pretty common, then. Thanks for the suggestion, I'll look into it more. –  Zong Zheng Li Oct 12 '12 at 14:43

3 Answers 3

up vote 9 down vote accepted

A common workflow to track down deep-sleep / wake-lock issues:

  1. Install CpuSpy
  2. Install BetterBatteryStats
  3. Turn off your phone
  4. Fully charge it while turned off
  5. Unplug the cable
  6. Start the phone, unlock it and open some apps like email, browser, facebook, and close them again
  7. Don't touch your phone, let it be on your table for a hour
  8. Open CpuSpy
    • "Deep Sleep" should be the longest bar of all. If not, the CPU works because a process (App, Service) constantly wakes your phone up or you use a non standard Kernel/ROM which has a Deep Sleep problem
  9. Open BetterBatteryStats
    • Set the first dropdown to "Kernel Wakelock" and second to "Since unplugged", then see if any app you've installed appears in the list, using high % numbers (waking your phone up)
    • Then set the first dropdwon to "Partial Wakelocks" and check again for any app waking your phone up with a high % number
  10. Uninstall the app which causes wake locks (preventing your phone from deep sleep)
  11. If the problem still persists, google for further instructions with the following pattern:
    • "wakelock + [appname]" without the brackets, enter the app or service name which causes high percentages in BetterBatteryStats, and google without the quotes!
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This is great, it's a nice and simple way to diagnose the problem. Seems the only solution is uninstalling, though, which doesn't help when system apps are responsible. –  Zong Zheng Li Oct 16 '12 at 21:34
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@ZongLi - By the way, it is usually the case that if an answer is good enough to be accepted (the tick) then it should be good enough to deserve an up vote (This answer is useful), so you might want to click on the up arrow whenever you click on the tick, so people feel appreciated. *8') –  Mark Booth Oct 17 '12 at 16:37
    
INFO: There are apps that work correctly, but missbehave because of some special case. For example my Google+ had constant wakelocks which drained my battery on maximum 1600 MHz constantly! In the settings I saw, that I've activated Google+ automatic Photo backup/upload. 2 days ago I clicked "Backup all photos from this device" to trigger a full upload of all the photos. One of the photos had a problem and it made the Google+ constantly trying to upload this photo in an infinite loop. The solution here wasn't to uninstall the app, but to futher investigate, WHY the app triggered a wakelock. –  Underlines Sep 27 '13 at 9:02

For non-techies, I recommend an app I develop called Wakelock Detector.

Check out this presentation, Android Wakelock Explanation, for more info about the "wakelock mechanism" in Android.

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You only have two answers on Stack Exchange, both to promote this app. If this is your app, you must disclose this in your answer or it will be removed as spam. –  Dan Hulme Jul 4 '13 at 8:32

You don't neccessarily have to uninstall the app. There times where there is a good reason for an app to keep your phone from sleeping. For example, I changed my login to my work email but forgot to update the email app on the phone that accesses my work email. It kept trying to login to sync and that was using up my batt charge.

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How does this answer the question? It says that the Android System was draining the battery. Zong did not even mention uninstalling an app. How is this "answer" helpful? –  ZnewmaN Apr 5 '13 at 22:25

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