Robbie Mosaic's Web Log

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Decheng “Robbie” Fan 2015-04-08

First of all, Surface Pro 3 supports Connected Standby, a mode that was not supported in earlier versions of Surface Pro.

Secondly, with Connected Standby, the only power plan available is Balanced. No “High Performance”, no “Power Saver”, no “Always On”.

Thirdly, many power plan options are hidden, and are only visible when you run the “powercfg /query” command. For example, to set display auto-turn off, you have to use the sleep timeout. This means, if the display is automatically turned off, the computer goes to sleep at the same time. Another setting that is not available is the CPU maximum (minimum) state. This was used to limit the CPU clock speed (for example, letting a 2.2GHz CPU run at 800MHz). Now, the CPU always runs in “adaptive” mode, which means the clock speed goes up and down based on actual usage. Hibernation timeout is also not visible.

Windows battery meter (on the task bar) doesn’t show the estimated remaining battery time. In order to view estimated remaining battery time, I need to install a third-party software. Currently I use BatteryBar free edition (although the Pro edition has more features, for the purpose of viewing the remaining time, the free edition is enough).

So, there are the following tips to save power:

1. It is very important to suspend or close applications that are CPU- intensive. To discover this, Process Explorer is very helpful. It can not only display CPU percentage, but also display CPU time. By sorting processes on the “CPU time” column descending, we can easily discover what processes used a lot of CPU. For short-running applications, the “CPU percentage” column is more useful, of course. For unrecognized processes, I can try to find its parent process, in order to determine what it does, and how it can be closed or whether it can be safely terminated or suspended. In addition, Windows services are displayed in a tooltip when hovering the mouse over a service process in Process Explorer. Note that do not do this on critical system processes (an incomplete list: System Idle Process, dwm.exe, Interrupts, System, explorer.exe, ChsIME.exe, MsMpEng.exe, WWAHost.exe, procexp64.exe, csrss.exe, lsass.exe, smss.exe, svchost.exe, taskhostex.exe, TabTip.exe, conhost.exe, services.exe).
2. The display brightness of course affects power consumption, too.
3. The web browser is also a source of power consumption, due to possible dynamic contents (javascript, Flash, etc.). Try to close as much unused tabs as possible. Also, the Metro version IE (or in future, Spartan) would help reduce power consumption as it is aware of the use case of tablets, so that background content is automatically suspended.
4. Although Microsoft claims that Connected Standby consumes only very little power in the background, it may still accumulate to 2% per hour in the case of Surface Pro 3. On my previous Surface RT, it usually consumes only 0.5% per hour, so the situation is not so good on the Pro version. To help reduce this kind of power consumption, there is a trick: actually Surface Pro 3 does support hibernation. Using the system “shutdown /h” command or my “sushiber -h” command can put the tablet into hibernation. Due to a special design in Windows 8.1, the hibernation and resumption are much faster than in Windows 7 (maybe by not performing data compression when writing to the disk?), although there are 8GB of RAM.
5. Note that besides pushing the power button, there are two other cases under which the tablet can be awaken. One is through opening the type cover. The other is by connecting the power cord. To avoid awaking through the type cover, go to Device Manager, Keyboards, Surface Type Cover Filter Device. Open the properties dialog, and go to the “Power Management” tab. Deselect “allow this device to wake up the computer” and confirm.
6. To avoid switching off the display (and going into sleep mode) when the type cover is closed, in Power Options, choose the desired power plan (such as “Balanced”, or a newly created plan), and choose “change advanced power settings”. Then, under “Power button and lid”, “On closing the lid”, “Battery/AC power”, choose “do nothing”. Of course, in order to save power, you would like to manually hibernate it when it is not used for long.

The maximum attainable battery life as I tested Surface Pro 3 is 8.5 hours, with the lowest display brightness. But, raising the brightness doesn’t affect power consumption too much, so it is OK to do so, to protect your eyes.