Nice Mart! Just to elaborate a bit more...

 Code:
[postprep]If UsingBattery()
   ? "on battery power"
Else
   ? "plugged in"
Endif

get $

Function UsingBattery()
   $objWMIService = GetObject("winmgmts:\\" + @WKSTA + "\root\wmi")
   $colItems = $objWMIService.ExecQuery("Select * From BatteryStatus Where Voltage > 0")
   For Each $objItem in $colItems
      $UsingBattery = IIF($objItem.PowerOnline,0,1)
   Next
EndFunction

Edited by ShaneEP (2012-04-23 10:39 PM)