Chapter 34 · Power Management

Practical Lab: Power Management Exploration

5 min read

Objective

Find out how your own PC handles power: which sleep states it supports, which power plan it uses, what is keeping it awake, what woke it last, which devices can wake it, and how healthy its battery is. You only look. Nothing in this lab changes a setting, and you will not run any shutdown, restart, hibernate or sleep command.

Time: 25-30 minutes
You need: A Windows 10 or 11 PC. A laptop is best (Part 6 needs a battery). No extra software.

What to Open

ToolHow to open it
PowerShell or Command PromptPress Win, type PowerShell (or cmd), press Enter (normal window)
Administrator window (only for optional steps)Press Win, type PowerShell, right-click it, choose Run as administrator
Control PanelPress Win + R, type control, press Enter
SettingsPress Win + I
Task ManagerPress Ctrl + Shift + Esc

Part 1: Which Sleep States Does My PC Have? (Section 2)

powercfg /a
  1. Is Standby (S3) listed as available? ________________
  2. Is Standby (S0 Low Power Idle) listed? ________________ (If yes, your PC uses Modern Standby, Section 5.)
  3. Is Hibernate available? ________________
  4. Is Fast Startup listed as available? ________________
  5. Pick one state that is not available. What reason does the text give? ________________

Part 2: Which Power Plan Is Active? (Section 7)

powercfg /list
powercfg /getactivescheme
  1. How many plans are listed? ________________
  2. Which one has the *? ________________
  3. Copy the GUID of the active plan: ________________

Part 3: See the Plan in the Graphical Tools

3A. Control Panel. Open Control Panel → Hardware and Sound → Power Options. Look at the plans shown. Click Choose what the power buttons do and note, without changing anything:

  1. What happens when you press the power button? ________________
  2. Is Fast Startup (under Shutdown settings) ticked, unticked or missing? ________________

(Close the window without clicking "Save changes".)

3B. Settings. Open Settings → System → Power & battery (on Windows 10: Power & sleep). Note:

  1. The screen and sleep timeouts (on battery and plugged in): ________________
  2. The Power mode shown (Best power efficiency / Balanced / Best performance): ________________

Part 4: What Is Stopping Sleep? (Section 3.6)

powercfg /requests

This may say "access denied" in a normal window. If so, either skip this part or run it from an administrator window (it only reads).

  1. Does any item appear under SYSTEM, DISPLAY or EXECUTION? ________________
  2. If yes, which program or driver is named? ________________

Part 5: What Woke the PC Last, and Who Is Allowed To? (Section 10)

powercfg /lastwake
powercfg /devicequery wake_armed
powercfg /waketimers
  1. What does /lastwake report? ________________ (It can say it is unknown, or show a timer or device; after a full restart there may be nothing useful.)
  2. List two devices in wake_armed: ________________
  3. Are there any wake timers? ________________

Look in Device Manager (Chapter 14). Open Device Manager (Win + X), expand Keyboards, double-click your keyboard, open the Power Management tab (if it has one) and look only at the Allow this device to wake the computer checkbox. Then press Cancel.

  1. Is your keyboard allowed to wake the PC? ________________

Part 6: Battery Health (Laptops Only) (Section 9)

powercfg /batteryreport

The command prints a file path, usually ending in battery-report.html. Open that file in your browser (copy the path into the browser's address bar, or find the file in File Explorer). On a desktop PC it will say no battery was found: skip this part.

  1. Design capacity: ________________
  2. Full charge capacity: ________________
  3. Health = full charge ÷ design × 100: ________________ %
  4. Cycle count (may be blank): ________________

Part 7: Watch the CPU Change Speed (Section 8)

Open Task Manager → Performance → CPU (Chapter 11). Watch the Speed number for 30 seconds while doing nothing, then open a few browser tabs or a video and watch again.

  1. Idle speed: ________________ GHz Busy speed: ________________ GHz

Part 8 (Optional, Needs Administrator): An Energy Report

In an administrator window:

powercfg /energy

It watches the PC for about 60 seconds (leave the PC idle), then writes energy-report.html and prints where. It reports possible power-wasting problems, as errors, warnings and information. Open the file and read the Errors and Warnings. It does not fix or change anything.

Part 9 (Optional, Needs a Modern Standby PC): Sleep Study

powercfg /sleepstudy

If your PC uses Modern Standby, this writes an HTML report about battery use during "sleep" (hedge: it may say it is not supported on your PC).

What You Must NOT Do in This Lab

Do notWhy
Run shutdown or click Sleep/Hibernate/Restart/Shut down to "test"It ends your session and you could lose work
Run powercfg /h off or onChanges hibernation and Fast Startup
Tick or untick boxes in Device ManagerCan break wake behaviour
Change or delete power plansNot needed

What Should Happen

  • Part 1 lists S3 or Modern Standby, and Hibernate.
  • Part 2 shows one active plan, marked with *.
  • Part 3 shows the same settings as the commands, in a graphical form.
  • Part 5 shows only a few devices (keyboard, mouse, network) allowed to wake the PC.
  • Part 6 shows the battery's full charge capacity at or below its design capacity.

Interpretation Guide

What you seeWhat it means
"Standby (S0 Low Power Idle) Network Connected"Modern Standby: phone-like sleep (Section 5)
"Standby (S3)"Classic sleep (Section 3)
"Hibernation has not been enabled"No hiberfil.sys; no hibernate or Fast Startup
Balanced plan with *The normal default
/requests lists a video player under DISPLAYThe player is keeping the screen on
/lastwake shows a timerA scheduled task or maintenance woke it (Section 10.3)
Health below about 80%Battery is worn; expect shorter use
CPU speed rises under loadP-states and turbo in action (Section 8.2)

Follow-Up Questions

  1. Your PC shows "Standby (S0 Low Power Idle)" and not S3. What does that tell you about how it sleeps and what could happen to the battery in a bag?
  2. /lastwake blames a timer. Where would you look for the cause?
  3. The battery report shows 36,000 mWh full charge and 45,000 mWh design. What is the health?
  4. Why should you not turn off Hibernate just to "tidy up"?
  5. Which command do you use first when a PC will not go to sleep?