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Power testing

Modern mobile computers are sold with an advertised battery life, ranging from a few to tens of hours. Nonetheless, when these devices are used on a daily basis, many users report the actual battery life doesn’t match up with the advertised numbers. For Chrome OS devices, we wanted to try to report battery life that was as close to what an average user experienced as possible.

The power_LoadTest was created to emulate average user behavior and measure the resultant battery life. The test is implemented as an open source Chrome extension which anyone can install and run.

The power_LoadTest is run as a series of one hour long iterations until battery exhaustion. Within each iteration, a load mix known as “60/20/10/10” is run:
  • [First 60% of the test] Browsing: a new website is loaded every minute.  The web page loaded is scrolled down one page (600px) every 10 second, then scrolled back up at the same rate.
  • [Next 20%] Email: Gmail is loaded in the foreground tab and audio is streamed from a background tab.
  • [Next 10%] Documents: Various Google Docs are loaded.
  • [Final 10%] Video: A full screen 480p YouTube Video is played.

The parameters of the test are as follows:
  • Backlight: Set to 40% of panel brightness.
  • Power management:
    • Dimming, blanking the screen and transitions to suspend-to-RAM state are disabled.
    • Ambient light sensor readings ignored.

The parameters of the system under test are as follows:
  • Battery:
    • Device only powered by battery (no AC power).
    • Battery charged to 100% prior to initializing test. Test continues in 1 hour iterations until battery passes low threshold (currently set at 3%). Initial & remaining battery charge is recorded.
  • USB: No external devices connected
  • Network: Device is associated with a wireless access point via WiFi.

Throughout the duration of the test, there are 5 sites loaded in background tabs. These sites were chosen to represent typical actions of a user on a daily basis:
  • Searching
  • Reading news
  • Checking on finance
  • Shopping
  • Communication

If you are interested in running power_LoadTest on a Chrome OS system, you will need a Chrome OS image that has been modified to run tests.  If you would like to reproduce reported battery life numbers, please ensure that your system under test matches the parameters outlined above.

While the initial version of power_LoadTest seems to emulate well what users experience every day on Chrome OS devices, this test will be constantly improved. As we learn more about how users use Chrome OS devices and how experienced battery life differs from tested battery life, we will use this data to refine the test, potentially changing the load mix or the parameters of the test.

Our goal is to ensure that when you purchase a device, you know - with reasonable certainty - how long that device will last in your daily use.


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