How can I find out when my laptop was last unplugged in windows 10?

You can generate a battery report which will contain this information. It's a manual process good for one-time checks, but not great for on-going repeated checks.

The process is simple.

1. Open a Command Prompt as Administrator.
2. Type in powercfg /batteryreport /output "C:\batteryreport.html" and hit Enter.
3. Open the report file using a web browser.

The report will contain history of the power states of your computer and the power source during that state.

Note: I got this information from a quick Google search and this helpful document which has lots of pictures: http://www.windowscentral.com/generate-battery-report-windows-10 I tested it myself on a Windows 10 tablet running build 1607 (Anniversary Update).

I need to know how long my laptop has been unplugged

Windows doesn't log any events when a laptop is unplugged.

You can however use something like the batch file below and create a custom event.

---

Battery.cmd

This batch file monitors whether a laptop is currently on mains power or battery power.

It creates a user defined event if the mains is unplugged and the laptop starts to use the battery.

@echo off
setlocal EnableDelayedExpansion
:start
rem get the battery status, 1 = battery discharging 2 = on mains
rem use findstr to strip blank lines from wmic output

for /f "usebackq skip=1" %%i in (`wmic path win32_battery get batterystatus ^| findstr /r /v "^$"`) do (
  set _status=%%i
  if [!_status!] equ [1] (
    rem on battery
    rem create a custom event in the application event log
    rem requires administrator privileges 
    eventcreate /l APPLICATION /t WARNING /ID 999 /D "Mains has been disconnected"
    goto :done
    ) else (
    rem on mains
    rem wait for 10 minutes then try again
    timeout /t 600 /nobreak > nul
    goto :start
    )
  )
:done
endlocal

Notes:

• The Eventcreate command works on Windows XP up to and including Windows 10, it requires administrator privileges to work
• If the mains is disconnected an event with ID 999 will be generated in the APPLICATION event log with the description Mains has been disconnected
• Modify the eventcreate command as required for your situation.
• Modify the timeout delay as required for your situation.

Example output

When running Battery.cmd and disconnecting the mains power the following output is generated:

> battery

SUCCESS: An event of type 'WARNING' was created in the 'APPLICATION' log with 'EventCreate' as the source.

>

And here is the new entry in the Event Log:

---

Further Reading

• An A-Z Index of the Windows CMD command line - An excellent reference for all things Windows cmd line related.
• eventcreate
• Using Windows PowerShell to Determine if a Laptop Is on Battery Power
• wmic - Windows Management Instrumentation Command.