Powershell script for getting the uptime of multiple Windows servers using WMI : http://wragg.io/get-uptime-from-multiple-servers/

Get-Uptime.ps1

#Requires -version 2.0
[CmdletBinding()]
param (  
    [ValidateSet("London","Berlin","Tokyo","")][string]$location
)

Write-Host ("`n" * 5)
Import-Module ActiveDirectory -Cmdlet get-adcomputer  

$Servers = get-adcomputer -filter {Enabled -eq $true -and OperatingSystem -Like "Windows*"} -property Enabled,OperatingSystem | ?{$_.DistinguishedName.contains($location)} 
$Errs = @()

$Count = 0

$Servers | ForEach-Object{
    $computer = $_
    $ErrMsg = $null

    Write-Progress -Activity "Attempting to get uptime value for $($computer.name)" -Status "$Count of $($Servers.Count) completed" -PercentComplete ($Count/$Servers.Count*100)

    If(Test-Connection $computer.name -TimeToLive 5 -Quiet -Count 1 -ErrorAction SilentlyContinue){

        If($os = Get-WmiObject -ComputerName $computer.name win32_operatingsystem -ErrorAction SilentlyContinue){

            $Uptime = (Get-Date) - ($os.ConvertToDateTime($os.lastbootuptime))
            $Display = "Up " + $Uptime.Days + " days, " + $Uptime.Hours + " hours, " + $Uptime.Minutes + " minutes"

            Write-Verbose  "$($computer.name) : $($computer.operatingsystem) : $Display"
            New-Object -TypeName PSObject -Property @{Name=$computer.name;OS=$computer.operatingsystem;Uptime=$Display;Days=$Uptime.Days;Hours=$Uptime.Hours;Minutes=$Uptime.Minutes;}

        }Else{$ErrMsg = "Failed to get uptime"}

    }Else{$ErrMsg = "Failed to ping"}

    #Trap Error
    If ($ErrMsg -ne $null){
        $Err = New-Object System.Object
        $Err | Add-Member -type NoteProperty -name Name -value $computer.name
        $Err | Add-Member -type NoteProperty -name Error -value $ErrMsg
        Write-Warning "$($Err.Name) : $($Err.Error)"
        $Errs += $Err 
    }

    $Count++

} | Select Name,OS,Uptime,Days,Hours,Minutes | Sort Days,Hours,Minutes -Descending | Export-Csv "Uptime-$location-$(get-date -format yyyy-MM-dd).csv" -NoTypeInformation

#Write Errors to file
If ($Errs -ne $null){$Errs | Select Name,Error | Export-Csv "Uptime-$location-$(get-date -format yyyy-MM-dd)-Errors.csv" -NoTypeInformation}