"Keep Wifi on During Sleep = Never" battery problem

Executive summary = You always want "Keep Wifi on During Sleep" set to "Always" if you care about your battery life.


In post #17 in the "P6210 - Huge Battery Drain on ICS" thread iosandroid found that setting "Settings->Wifi->Menu->Advanced->Keep Wifi on During Sleep" to "Never" caused battery drain. Since I feel this is big bug and my mom told me I'm special I thought I'd start a new thread with some more details on this problem, a more descriptive thread title to highlight this issue and a few questions of my own.

I have a Samsung Galaxy Tab 7.0 Plus (aka GT-P6210) WiFi only tablet that had HC (Honeycomb) when I first got it. To save battery I changed "Settings->Wifi->Menu->Advanced->Keep Wifi on During Sleep" to "Never" (actually think the wording was a little different back in the HC days, but you get the idea). I'm not sure if/how much this helped, but it didn't hurt my battery life.

Shortly after upgrading to ICS (Ice Cream Sandwich) I noticed my battery life was worse. Apparently I wasn't alone since "iosandroid" (see above) had the same problem and solution. That is, if you set Settings->Wifi->Menu->Advanced->Keep Wifi on During Sleep" to "Never" or "Only when plugged in" your better drains much faster when you're tablet is idle. How much faster? In my tests setting this to "Never" drained my battery by 3.10%/hour. If I leave this at its ICS default of "Always" my battery only drains at 0.27%/hour, OVER 10 TIMES BETTER (idle) BATTERY LIFE! See the bottom of this post for a listing of my battery drain tests.

By using "CPU Spy" I could see that with "Keep Wifi on During Sleep" set to "Never" my tablet would never go into deep sleep, but with it set to "Always" my tablet would spend almost all of its time in deep sleep. GSam Battery Monitor showed that "Kernel (Android OS)" was using up most of my battery when this problem is occurring.

This problem isn't limited to ICS, I also got the same results with JB (Jelly Bean). Specifically I used "AOKP Jelly Bean Milestone 1". With stock ICS the default setting is "Always", so only people that mess with their advanced settings will be affected by this. Note that I believe that an OTA upgrade from HC to ICS will retain your previous settings for this. In JB (at least AOKP JB), this problem will have a much wider reach since "Keep Wifi on During Sleep" defaults to "Never".


Now on to my questions:
-Does anyone know the scope of this bug? Does it only affect the P6210, or Samsung devices, or every Android device? iosandroid reported having the same problem with his phone.
-Do I have to open a tech support case with Samsung to report this bug, or is there a better way?



[Battery Drain Tests]
VERSION Keep Wifi on During Sleep? DRAIN RATE
----------------------------------------------------------------------------------------------
HC Always 1.00%/hour (lost 2% total over 2 hours)
HC Never 0.50%/hour (lost 1% total over 2 hours)
ICS Always 0.27%/hour (lost 2% total over 7.5 hours)
ICS Never 3.10%/hour (lost 24% total over 7.75 hours)
JB Always 1.0%/hour (lost 1% total over 1 hour)
JB Never 3.52%/hour (lost 81% total over 23 hours)
-Legend
--HC = Stock Honeycomb (Android 3.2)
--ICS = Stock Ice Cream Sandwich (Android 4.0.4)
--JB = AOKP Jelly Bean Milestone 1 (Android 4.1.2)
-Setting "Keep Wifi on During Sleep?" to "Only when plugged in" behaves the same as "Never" (i.e. it has same battery drain problem)
-Yes, I know my testing time periods vary wildly, but I'm too impatient to wait a day for each of the tests. For example I'm sure JB's "Always On" loss rate is much closer to ICS's.

Airplane mode uses more battery than WiFi always on

viper001 said:

Try doing your test in Airplane mode

Click to expand...

Click to collapse

Yup, my tab is WiFi only. However I did actually test it in airplane mode and found that the battery lost 0.40%/hour (lost 11% total over 27 hours) with airplane mode enabled. This is still worse than the 0.27%/hour you lose when you just leave WiFi on (Keep Wifi on During Sleep? set to Always). This airplane mode battery drain was also unexpected to me, but in googling it seems like this is a common problem.

One last test I did was to manually turn the WiFi off. When I did that the battery only drained at a rate of 0.11%/hour (lost 1% total over 9.5 hours). I should test that longer to get a more precise number, but my short test was good enough to show that manually turning WiFi off does actually save power (it's about time something worked as I expected it to .

My next planned test it to use something like AutomateIt to automatically turn off the WiFi after the screen turns off to see if I can automate the WiFi battery savings.

As Krusty the Clown says, "it's not just good--it's good enough"

viper001 said:

If you know how, try looking into the build.prop. you'll find that stock wifi. supplicant_scan_interval=15. try a higher number like 90 or 180. this basically lengthens the time for wifi network searches from 15 secs to 90 or 180 seconds respectively.

Click to expand...

Click to collapse

I could probably figure out how to change that, but I've decided that just leaving WiFi on all the time gives me good enough battery life. I enjoy troubleshooting these types of technical problems, but unfortunately I must return to debugging my three year old daughter's Dravet Syndrome. Her cognition is deteriorating, so I'm hoping to find a solution or workaround soon. If any of the multimillionaires that read this forum want to fund a cure for Dravet Syndrome, head on over to dravet.org or dravetfoundation.org

neu - smurph said:

I've got this issue on a Chinese Tablet running JB 4.1.1. After some investigation the conclusion I've reached is that the settings are mislabled on the GUI. "Always" results in disconnection from the SSID 15 minutes into sleep (although WIFI is still 'ON'). "Never" keeps WIFI on and connected indefinitely, and if autosync is also on you'll get lots of wake-locks and reduced standby battery life, particularly if you have location reporting on and google maps installed.

Click to expand...

Click to collapse

Interesting results, but that wasn't my experience. For example with WiFi always on my tablet does stay connected to the network all the time. All of these weird issues is about enough to make you want to buy an iPad.