When did WiFi start working in the background on Windows Phone?

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.

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.