PlayBook: Power Consumption

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I've been taking power consumption measurements while running the PlayBook under various loads, and some of the results are pretty interesting. I'll write up more later, but here's an initial overview of some data that may be useful to you, either as a user, or as a developer.

First a bit of background. The PlayBook has two battery packs in it, with the combined pair providing nominally 5400mAh, which at an average voltage of 3.7V provides 19.98Wh of energy. See for example the teardown for some pics of the labelling.

In actual fact, Lithium-Ion Polymer batteries never provide the full rated capacity and, at least in the case of my own PlayBook, I can confirm that the capacity as shipped was only around 93% of that. The initial drop can be disconcertingly rapid, too, and after 42 recharge cycles their capacity is now only 90%, or about 18Wh.

That Watt-hour capacity value can tell you roughly how long a battery will run your device by dividing by the average power used. If, for example, the device used 1W on a continuous basis, 18Wh would give 18h of use.

A PlayBook, sitting idle but with the screen turned on, backlight at 50%, running no apps, uses about 2.3W. That means even if you basically didn't do anything useful with it, you'd get only about 7.8h under those conditions. There's a reason the screen and backlight turn off so quickly!

Here are some other basic numbers for you to compare. The values shown are in milliwatts (50mW is the same as 0.05W). The "Life at Constant Load" value is an approximation based on a battery at 90% health, which is probably typical for most PlayBook owners as of this date.

Power consumption (in mW) under different loads for PlayBook
Load Power Life at Constant Load
Standby 52mW 15 days
Screen on/backlight 0% 1680mW 10.7h
Screen on/backlight 50% 2300mW 7.8h
Screen on/backlight 100% 3000mW 6.0h
Standby/White Noise on/volume 50% 360mW 50h
Standby/GPS @2Hz 213mW 85h
Video 720P/volume 0%/backlight 30% 2300mW 7.8h
Video 720P minimized/volume 10%/backlight 100% 3500mW 5.1h
Video 720P fullscreen/volume 10%/backlight 100% 3240mW 5.6h
Flash video on CNN site (not fullscreen)/backlight 100% 4000mW 4.5h

The White Noise app mentioned there is my own, available from App World. It's written "properly" so it will generate smooth, pure, non-repeating random noise even when the PlayBook is on standby, just as you'd want for masking background noise and letting you get a good sleep!

The most interesting results so far are that the GPS consumes so little power (yay!) and that the backlight and screen together consume so much. It also appears that playing fullscreen video uses less power than running it in a web page or with the video player app minimized (but active). I need more measurements to say for sure but it looks like this holds true whether it's a Flash player in the browser or the standard video player.

Advice for maximizing battery life? Keep the screen off as much as possible! Set the timeouts for as short as you can live with and make liberal use of that shiny new "Stand By" button found in the System Tray battery popup.

If you have to actually use the screen (i.e. for most real uses), keep the backlight as low as possible. Depending on lighting conditions, you may find that having the backlight at minimum is acceptable, or as low as 25% may be okay.

Finally, run video fullscreen where possible.

So, who wants a battery monitor app? You won't find anything better than Battery Guru for the BlackBerry PlayBook. :-)

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