Saturday, September 1, 2012

Dell Sputnik: Battery Life Test

After I got the Sputnik set up the way I wanted I figured it was time to test the battery life, so yesterday afternoon I unplugged the power cord and did normal "work stuff" to see how much time I'd get out of the battery under normal working conditions.

Note that I'm not a professional hardware tester or benchmarker, so this was not a scientific experiment resulting in reams of data that can be sliced and diced 100 different ways. To me those charts and graphs always seem artificial anyway (though I suspect it's quite efficient to do things that way if you test hardware for a living), so my methodology was, quite simply, to use the laptop unplugged until the battery ran out.

Applications Running During Testing

As far as specifically what I was doing and what applications I had running, I was doing Python/Django development yesterday, so here's what I had running:
  • Emacs
  • Sublime Text 2
  • MySQL
  • Chrome with 6-10 tabs open
  • Terminal with 3-4 tabs open
  • Pidgin IM client
  • WiFi
  • Bluetooth (I didn't use this, but it's on by default so it was running)
I intentionally did not dim the screen to its lowest usable setting since I didn't want to skew the results too much. I just left the screen brightness at the default setting and let it automatically increase and decrease the brightness based on the default power settings.

I also did not (and I don't even know if you can do this now that I think about it) disable the backlighting on the keyboard, so it would turn on and off depending on the ambient lighting at any given time.

Testing Process

As I alluded to above you won't find a lot of scientific methodology here, but I figured I'd say a couple of words about what I did specifically during the battery drain period.

If you're a developer you'll already know the gist of this, but basically I was hopping back and forth between Emacs and Sublime Text 2 (I was working on converting a CFML application to Python and it was easier to have the CFML app up in Sublime and do the Python work in Emacs), the browser, and the terminal to run scripts or do something in MySQL. I also would start/stop the Django application, which is basically a little web server. (I did not install Apache on this machine yet since I'm pondering switching over to Nginx anyway.)

Also I'd occasional get up to get a cup of coffee, etc. so there were brief periods here and there when I wasn't using the machine at all, but not so long that it went into hibernation mode.

That's about it for the process discussion -- I just used the thing as I normally would any computer on a normal work day.

Observations

With the default power settings the Sputnik did a great job of being efficient without being annoying. The screen would dim after a couple of minutes if I was reading something and not typing or using the touchpad and it would raise the brightness again once I moved the mouse or typed. I mention this because some machines I've had in the past were extremely aggressive with power-saving functionality (constantly "strobing" or adjusting the screen brightness, for example) to the point of me having to turn off the power management altogether which kind of defeats the purpose. So the default settings on this machine with Ubuntu work quite well.

Taken on balance the time remaining in the battery monitor was quite accurate, though I did notice it would jump up when I was doing something like reading and not interacting with the machine. For example I'd bring up a tab in Chrome with something I needed to read, and immediately after doing that I'd check the time remaining and let's say it said I had 3 hours left. After reading something (i.e. not typing or moving the mouse) I'd check the time remaining again and it'd say I had 6 hours left. Then after using the machine for a minute I'd check again, and it'd be back to the original number of about 3 hours.

I have no engineering rationale to back this up, but as I was seeing this behavior I likened it in my head to the real-time gas mileage gauge in a car. If I'm braking down a hill in my Prius, it'll tell me I'm getting "infinite" miles per gallon, which is basically a projection based on what's going on at that point in time. The battery meter seemed to be behaving similarly, projecting battery life based on the activity at a given moment.

Taking the high estimation outliers out of the equation, however, it was quite accurate, even down to the warnings at the end when the battery meter (and the light on the front of the computer, which is a nice touch) turned red. On some machines I've had in the past when it says you have 20 minutes left, that may turn to a "plug it in right now" message in about 5 minutes, but that didn't happen here. When it said I had 17 minutes left, it meant I had 17 minutes left.

Hibernation

If you know anything about running GNU/Linux on laptops you'll know that hibernation working correctly can be a bit of a problem if the hardware and drivers don't play nicely together.

I'm happy to report that the hibernation function on the Sputnik works exactly as you'd expect -- you simply close the lid, and a few seconds later the light on the front of the machine will start flashing slowly, indicating it's in hibernation mode. When you re-open the screen things come back quite quickly including reconnecting to WiFi, so there are no problems at all with hibernation.

Results

One more proclamation of how unscientific this was -- I didn't run a stopwatch while doing this. I just checked the time when I started and checked it again when the battery was more or less dead.

The results are quite impressive, with a run time of about 8 hours 20 minutes in my usage. The marketing materials for this machine claim between 8 and 9 hours so these numbers are quite legitimate in comparison to my usage, and if you disabled WiFi and Bluetooth and dimmed the screen, I can see pushing 9 hours of run time pretty easily.

This is all the more impressive when I compare it to my old Asus Eee netbook, which was a vastly less capable machine and would get 10 hours of battery life only with the larger 9-cell battery that not only stuck out the back of the machine like a tumor but also greatly added to the weight of the machine. So for the Sputnik to get this kind of battery life in normal usage in such a small, light package is really great.

Another big plus for the Sputnik!

I still haven't covered installation and some settings tweaks so I'll do that in another post soon.

3 comments:

Chris Sturgill said...

After installing the Sputnik image on our XPS 13, all was bliss. Except for the touch pad being nearly worthless.

Then the keys starting failing.

Call me old fashioned, but I need either the mouse or the keyboard to work.

And since this all failed in week five of ownership, and outside of the 21-day grace period, Dell won't take it back.

Any one want to buy an expensive paperweight?

Matt Woodward said...

Wow -- very odd. I haven't had any trouble with mine at all. Really sorry to hear that!

Toby Petty said...

Chris, Where are you based? If you're based in the UK, then you can demand a replacement under the Trade Descriptions act 1988. I'm not sure if there's any equivilent in the US/Canada