So I’ve had my Nexus 7 tablet for a while (a good companion to my iPhone ;-), and one of the things I’ve noticed is that the battery gets sucked dry while it is sleeping. I’ll start off with a fully-charged battery, then unplug it and use it for 5 minutes, and put it on the table, but don’t plug it back in. 24 hours later the battery is 1/3 to 1/2 used up. Wait 2-3 days and the battery is completely drained. Argh! Why is this happening?

I finally did some research, and found both the problem and the solution.

The hint on the problem came from a forum post I read. First, in the Settings app select the Battery – this will bring up the Battery view. At the top of the Battery view is a line graph that shows your battery level over time. Although there is no visual cue that you can do this, touch this graph. Now it brings up the History Details view for the battery. What you’ll see now is a larger line graph for your battery level over time, but more importantly is a breakout by category of what is using your battery: you should see entries for Wi-Fi, GPS, Screen, etc. Next to each entry is a segmented bar graph that shows when these entries were active over this time period. On my Nexus 7, the obvious top consumer of the battery was the Wi-Fi: it had a solid bar that indicated it was constantly in use, even while the tablet was asleep. There are no breaks in that bar. The line graph of the battery level showed approximately a 45 degree slope for the battery level, basically the battery getting sucked dry, apparently by the Wi-Fi. What is going on here?

Back in the main page of the Settings app, select Wi-Fi. Now select the rightmost icon in the top bar, the icon with the 3 vertical dots (like an ellipsis). That should bring up a context menu, one of the options is titled “Advanced”, meaning Advanced Wi-Fi Settings: select it and you’ll get a new screen. On this screen, one of the options is “Keep Wi-Fi on during sleep”. It is currently set to “Always”. Eh? That’s not what I want. Is that why my battery is draining during sleep, and the battery history indicates that the Wi-Fi is the function doing the draining? You betcha. Click on the “Keep Wi-Fi on during sleep” line and select a more reasonable value, such as “Only when plugged in”. Now back out of the Systems app. You’re done.

Now when I leave my Nexus 7 asleep and unplugged for a 24-hour period, the battery drains only a few percentage points, not 30% or 50%. This is the behavior I want.

I checked the same setting on my friend’s Nexus 7, and it had the same default. Why did Google choose to use this default? Maybe they want system updates to be downloaded in the background while the tablet is sleeping. Or maybe they don’t want the Wi-Fi to take 15 seconds to re-associate with the base station when I wake it up. Well, whatever the reason, it’s not worth my battery getting sucked dry when it is sleeping while it’s not plugged in. Bad default, Google.

But if that is the worst pain point on this tablet, then take that as a compliment. It is a good little machine.