I have been running overnight battery tests on my Surround using various scenarios for the past month, looking for apps or services that cause excess battery drain. But I digress already; back on topic. One of those tests involved running "WiFi Only", with Data and all Background Tasks disabled.

Although I was not paying much attention at 6:30am when I woke my phone from sleep to check my battery meter, the first time I ran the WiFi only test I thought I noticed a couple message indicators on my lock screen. I was a bit more prepared the next night, and even made sure to send each of my accounts a message about 30 minutes after setting my phone down in a WiFi only state. My overnight test involves leaving the phone untouched for 7.5 hours (about half a typical day) and checking the results in the morning. Sure enough, when I woke the phone in the AM, before WiFi could wake up, I saw indicators for messages on three of my Email accounts.

Winding down the battery testing, I ran WiFi only tests the past two nights (just to be absolutley sure), with my 7 Background Tasks enabled, to check battery drain and email delivery. As you can see from the screen captures, messages did make it through on both nights. Again, I sent messages to three accounts, 2 push and one every 30 minutes, about a half hour after setting my phone down. Although I sat next to my phone for at least another 30 minutes I never heard the new message tingle, suspecting that to preserve battery, maybe this "feature" works in stealth mode, delivering messages without any indicators. But last night, somewhere between 4:30 and 5:30am (should have written the time down, but too groggy) while rolling over in bed I heard a new message tingle from the other room. Sure enough, when I checked this morning, I got a message from Urban Dictionary, sent at 4:00am, along with a bunch of others sent at various times between midnight and 2:00am, including those I sent myself.

Screen Capture4 Screen Capture2 Screen Capture3

Based on my observations I don’t believe messages are pushed to the phone, but instead WiFi may somehow be turning on every 1 to 2 hours to fetch whatever is available. Btw, although it might be possible for WiFi to activate with an inbound Text that turns the screen on for a few seconds, the past two nights I had no overnight Texts, eliminating that scenario. Also, I ran at least a dozen "WiFi AND Data OFF overnight tests" and never received an Email, so no chance that Data is not really turning off. Back in the Pre-NoDo days, I did test out WiFi activity, putting my phone to sleep for 2+ hours, and never received a message. Either it wasn’t long enough or this is one of the 500 new Mango features we don’t know much about. As an FYI, when your Windows Phone is off charge (AC or USB) WiFi will disconnect about 30 seconds after you turn off your screen, unless it is actively downloading, streaming music, etc. In my tests, Background Tasks were enabled, but there were no applications running in the background.

I have tried to recreate this scenario in the office during the day, running WiFi only and setting the phone down for a couple hours at a time, but as Texts come in throughout the day, it’s a bit harder to verify, although more than once the Lock screen showed new Emails when the phone woke for a new Text message. And I think I may have come up with a way to check if Background Tasks are updating over WiFi. As they update so quickly once you wake up the phone, I will try to take a screen capture prior to starting the test and then power down my router "before" I wake up my phone in the morning and check the results. Should be interesting.

While WiFi updating in the background may be standard fare on other platforms, Windows Phone is all about saving battery power and improving performance, so this is a bit of a surprise. Oh, and speaking of the battery, after subtracting my "baseline" battery drain (more on that tomorrow), running WiFi along with 7 (actually 6) Background Tasks, my 7.5 hour overnight test consumed 3 to 4%. And note that’s with my 7 month old (I have two), heavily used (an average of 1.5 charges per day), wimpy 1230mAh battery. A new Titan has about 35% more juice, so a 2-3% drop might be expected.

Although I am on the grandfathered "unlimited" AT&T Data Plan, I know that 3G is gnawing at my battery throughout the day, which does bug me somewhat. Running WiFi only all day, with some occasional email/text reading & sending, along with some other tinkering, I only burnt up about 25% of my charge. A substantial difference. And should AT&T ever eliminate unlimited, I would have no problem surviving with the 200MB plan, knowing that WiFi could handle most of the heavy lifting, including background updates although somewhat delayed.

So is this something new, or am I just late to the party again. Sound off in the comments below.


  1. You do realize that there is a setting for each individual email account that you can set how often your email updates. You can have it to manual syncing and then it never receives new messages, even when wifi is on, until you sync your email.

  2. I believe it will have something to do with e-mail settings. If it set to every hour then i would expect the phone to try to.

  3. @Jason: Well, duh. Yeah, I sort of know that. This was a test so I was not trying to keep my mail from syncing automatically. I am trying to understand why it does with data turned off.

    @kevgallacher: Well, if that was the case, how would you explain the two push email accounts that “don’t check for mail every hour or so. Mail get’s pushed, but you need to have an open connection for that to happen.

    @markiz: Not so. WiFi only stays active on a Windows Phone when it is plugged in to a power source. While running on battery, it will disconnect approximately 30 seconds after you put your phone to sleep. Turn your data off now, turn WiFi on, and put your phone to sleep for a minute. When you wake it it you will see the WiFi icon reconnecting to your network.

    Or, while you phone is in WiFi only mode, put it to sleep and send yourself a push email. Wait ten minutes (you won’t get the message) and turn your phone on. As soon as WiFi reconnects, your message will come through.

    And if you were correct, why don’t push emails come over immediately as they always do when data is turned on. Also, consuming 2% of your battery over 7.5 hours, or 4% over a typical day would be extremely efficient for an “always on” WiFi connection.

  4. Ha ha love it when somebody knows what they are talking about. Keep up the great investigation work Jim.

  5. Hey,

    I noticed a similar activity on the Samsung Focus I got a few days ago.

    I have the device sit on my desk with 3g OFF and WiFi ON and it’s NOT connected to my computer or being charged.

    I didn’t get notifications and I wondered why; after some research I found out the WiFi goes to sleep when the screen is off. Well, no problem, I can live with that.
    Until one time I did get a notification when the screen was off (without getting a call/SMS) and I started to ponder what the hell is going on.
    So I decided to check my router logs during a time I was asleep and I saw some weird activity from my phone’s MAC address:
    * activity at 01:19:55 AM ~ around when I went to sleep.
    * activity at 04:05:26 AM
    * activity at 06:06:31 AM
    * activity at 08:07:36 AM
    * activity at 10:08:41 AM

    So it appears the device wakes up the WiFi every two hours when it’s not in use.
    I’d like to do some more testing on this to see if something is affecting it.

    I have the following settings/accounts:
    – two mail accounts (1 gmail and 1 hotmail); one is set to get mail “as it arrives” and the other is set to get it every 15 minutes.
    – facebook app is set to run under screen-lock (yet it doesn’t give notifications when screen is locked, how useful) and all notifications-types are marked with V.
    – background tasks are ENABLED.
    – battery save is OFF.


  6. Good observation and detail. Never thought to check my WiFi log for activity. The two hour cycle makes sense, as the one+ hour tests at my office didn’t always yield a positive result. Fyi, the three accounts on my lock screen include two push (Hotmail & Live) and one every 30 minutes (Yahoo). Also one other account that updates every 2 hours, but as I have to open the lock screen to see activity, can’t be 100% certain (but 95% for sure) that it also updated overnight. Background tasks and battery saver both enabled.

    Would be interesting to know how long the connection remains active while asleep, for example to allow for background task updates. If so, it’s almost feasible to go without data active (although somewhat delayed), when WiFi is available. An alternative for users on limited data plans or interested in conserving battery power.

  7. Yeah, it would be nice to know for how long it stays active. I’m trying to figure out how to do it.
    Anyway, I did another test today; this time I left the device hooked up to my PC with a data cable. The results on my WiFi activity changed –> It still sent a REQUEST even though it had a constant connection, but now it was every 1 hour instead of 2 hours.

    I suspect all of this has to do with the device checking for updates. It’s probably designed to check it every 2 hours when it’s not charged and every 1 hour when it is.
    I’m gonna do another test tonight but this time I’ll turn the “check for updates” option off and see what happens.

  8. Jim, danihh,
    any news on your investigation?

    I’ve experienced the same behavior on both my WP7 devices (HTC HD7 and Nokia Lumia 710).

  9. Hello there
    i have samsung omina w

    i have a strange issue

    usually the wifi turns off when in sleep mode
    and turns back when the screen is switched on again

    about the battery i get very poor battery in that case


    something strange happens

    sometimes when i look at the phone
    i see that the wifi was constantly on when in sleep (dont know how that happens)

    and when i look at the battery life
    its life gets doubled and it stays

    thats something really strange

  10. I do not understand one thing, I always get more battery when on wifi rather than on data network. Then what is the need for making wifi sleep and keeping data plan open? Is data network closed too when screen turns of?

  11. Don’t know about that one. So with both WiFi & Data turned on, you get better battery results than with Data only. I guess it could be possible, assuming you have a good WiFi connection and a poor Data connection. Maybe your phone does not have to work so hard to transfer data. Remember you have a phone and carriers “want” you to use as much data as possible, and then hopefully bill you if you go over your limit. So they never want you to turn Data off. WiFi on all the time would be a pretty big hit on your battery though. To answer part 3, Data is “always” on even when the screen is off. That’s how you get background tasks to update, email and other toast notifications to come in, etc.

    Guess I am going to find out about this later in the week. I have been using WiFi 24/7, with data turned on, as my 3G data connection was so poor, I could download much faster over WiFi. But now with LTE/4G on my Lumia 900, my lowest speed the past two weeks has been higher than my fastest WiFi speed. So I am going to turn off WiFi on the 26th (when my new month cycle starts on AT&T) and see how my battery drain changes going Data Only. Also curious to see how much data I am currently using. With my Unlimited plan, not too worried, but shouldn’t be much more than 2GB for the month.

  12. Thanks for the clarification. I use lumia 900 too, but no LTE in my area. Somehow I feel that battery is draining faster when the phone is idle. When i’m using the phone, no problem, its a lot better than what I expected and I use it mostly on Wifi at work and at home.
    Other than this one thing I’m absolutely loving this phone. Got it just 3 days back. By the way how did you get that network dashboard screen?

  13. Thanks for the nice read, Jim! So now for this one: I come home from work, toy around with my Lumia 800 for a while, using the WIFI connection. 3G is turned off. Now I put the phone aside. After 5 minutes, a friend sends me a whatsapp message… that never arrives! Only when I wake up the phone again it comes in. Making Whatsapp pretty useless as an application… Do you know of any way to solve that issue? Apart from turning on 3G that is, which I find quite useless when I am at home and able to use WIFI?


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