"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)
--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.