Use Powershell to insert LastBootUpTime into SQL table

Is there a way to find LastBootUpTime with Powershell and insert results to a SQL table with data type of smalldatetime?  I have attempted the following but receive error: 

Exception calling "ExecuteNonQuery" with "0" argument(s): "Conversion failed when converting character string to smalldatetime data type."
At C:\ServerUptime\ServerUptimePowershellScript.ps1:46 char:22
+  $cmd.ExecuteNonQuery <<<< ()
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : DotNetMethodException

Here is the code I have been trying.  I am new to Powershell and don't really know if I am doing FOREACH correctly.  The SELECT ServerName is returning a number of servernames.

# First, clear existing table
$ClearTbl = Invoke-Sqlcmd -Database DatabaseName -Query 'DELETE FROM [DatabaseName].[dbo].[ServerUptime]' -ServerInstance ServerName

# Output to SQL Server table
##Connect to the SQL server and the Database
 $conn = New-Object System.Data.SqlClient.SqlConnection("Data Source=ServerName; Initial Catalog=TableName; Integrated Security=SSPI")
## Open DB Connection
 $conn.Open()

# Get server names for net stats srv to loop through
$DataSet = Invoke-Sqlcmd -Database DatabaseName -Query "SELECT ServerName FROM [DatabaseName].[dbo].[TableName]" -ServerInstance ServerName

foreach ($element in $DataSet)
  {
  $element
  $Server = $element.ServerName
    
# Get server uptime and convert to SQL datetime format (2013-04-08 00:00:00.000).
$wmidate=(Get-WmiObject -Class Win32_OperatingSystem).LastbootUpTime
$shortdt=[System.Management.ManagementDateTimeConverter]::ToDateTime($wmidate).ToShortDateString()

foreach ($lastbootuptime in $wmidate)
{
$lastbootuptime
$uptime = $lastbootuptime

#Create SQL Insert Statement with your values
$insert_stmt = "INSERT INTO ServerUptime(ServerName,Uptime) VALUES('$Server','$uptime')"
 }
}
## Create your command
 $cmd = $conn.CreateCommand()
 $cmd.CommandText = $insert_stmt
## Invoke the Insert statement
 $cmd.ExecuteNonQuery()
## Close DB Connection
 $conn.Close()

Appreciate any help. Thanks!