@echo off & setlocal enableextensions
  set myvar_=My Test String!  åöä
  echo %myvar_%
  call :ToUpcase "%myvar_%" myvar_
  echo %myvar_%
  endlocal & goto :EOF
  ::
  :: ======================
  :ToUpcase
  setlocal enableextensions
    set var_=%1
    set var_=%var_:a=A%
    set var_=%var_:b=B%
    set var_=%var_:c=C%
    set var_=%var_:d=D%
    set var_=%var_:e=E%
    set var_=%var_:f=F%
    set var_=%var_:g=G%
    set var_=%var_:h=H%
    set var_=%var_:i=I%
    set var_=%var_:j=J%
    set var_=%var_:k=K%
    set var_=%var_:l=L%
    set var_=%var_:m=M%
    set var_=%var_:n=N%
    set var_=%var_:o=O%
    set var_=%var_:p=P%
    set var_=%var_:q=Q%
    set var_=%var_:r=R%
    set var_=%var_:s=S%
    set var_=%var_:t=T%
    set var_=%var_:u=U%
    set var_=%var_:v=V%
    set var_=%var_:w=W%
    set var_=%var_:x=X%
    set var_=%var_:y=Y%
    set var_=%var_:z=Z%
    set var_=%var_:å=Å%
    set var_=%var_:ä=Ä%
    set var_=%var_:ö=Ö%
    set var_=%var_:"=%
  endlocal & set %2=%var_%& goto :EOF

  @echo off & setlocal enableextensions
  set myvar_=My Test String!  åöä
  echo %myvar_%
  call :ToUpcaseWithFor "%myvar_%" myvar_
  echo %myvar_%
  endlocal & goto :EOF
  ::
  :: ======================
  :ToUpcaseWithFor
  setlocal enableextensions enabledelayedexpansion
  set var_=%~1
  for %%c in (A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Å Ä Ö) do (
    set var_=!var_:%%c=%%c!
    )
  endlocal & set %2=%var_%& goto :EOF

  @echo off & setlocal enableextensions
  set myvar_=My Test String!  åöä
  echo %myvar_%
  call :ToUpcaseWithGawk "%myvar_%" myvar_
  echo %myvar_%
  endlocal & goto :EOF
  ::
  :: ================================================================
  :ToUpcaseWithGawk
  :: Requires G(nu)AWK
  setlocal enableextensions
    gawk 'BEGIN{printf"@set var_=%%s\n",toupper(%1)}'>"%temp%\tmp$$$.cmd"
    for %%c in (call del) do %%c "%temp%\tmp$$$.cmd"
  endlocal & set %2=%var_% & goto :EOF

  @echo off & setlocal enableextensions
  rem The same with GnuWin32 gawk (let's call it unxgawk)
  set myvar_=My Test String!  åöä
  echo %myvar_%
  call :ToUpcaseWithUnxGawk "%myvar_%" myvar_
  echo %myvar_%
  endlocal & goto :EOF
  ::
  :: ================================================================
  :ToUpcaseWithUnxGawk
  setlocal enableextensions
  rem enabledelayedexpansion
    unxgawk "BEGIN{printf\"@set var_=%%s\n\",toupper(\"%~1\")}">"%temp%\tmp$$$.cmd"
    for %%c in (call del) do %%c "%temp%\tmp$$$.cmd"
  endlocal & set %2=%var_% & goto :EOF

  @echo off & setlocal enableextensions enabledelayedexpansion
  ::
  :: Constants for the lower and upper case
  set dn=abcdefghijklmnopqrstuvwxyzåäö
  set up=ABCDEFGHIJKLMNOPQRSTUVWXYZÅÄÖ
  ::
  :: Set a test string
  if "%~1"=="" (
    set Str=This is a test string
    ) else (
    set Str=%*
    )
  ::
  :: Get the length of the string assuming a max of 255
  set charCount=0
  for /l %%i in (0,1,254) do (
    set char=!Str:~%%i,1!
    if defined char set /a charCount+=1)
  ::
  :: Upcase character by character
  set StrUp=
  for /l %%i in (0,1,%charCount%) do (
    set char=!Str:~%%i,1!
    for /l %%p in (0,1,28) do (
      if [!char!]==[!dn:~%%p^,1!] set char=!up:~%%p,1!
      )
    set StrUp=!StrUp!!char!
    )
  ::
  :: Display the result
  echo %Str%
  echo %StrUp%
  endlocal & goto :EOF

  @echo off & setlocal enableextensions
  if defined ProgramW6432 (
    echo/
    echo Exiting: %~f0 is incompatible with 64-bit Windows (but read on)
    goto :EOF)
  ::
  set myvar_=My Test String!  åöä
  echo %myvar_%
  call :ToUpcaseWithSed "%myvar_%" myvar_
  echo %myvar_%
  endlocal & goto :EOF
  ::
  :: ====================================================================
  :ToUpcaseWithSed
  :: Requires SED
  setlocal enableextensions
  for /f "tokens=*" %%f in ("%temp%") do set temp_=%%~sf
  echo @set var_=%1^
    |sed "y/abcdefghijklmnopqrstuvwxyzåöä/ABCDEFGHIJKLMNOPQRSTUVWXYZÅÖÄ/"^
    |sed -e "s/\"//g">%temp_%\tmp$$$.cmd
  for %%c in (call del) do %%c %temp_%\tmp$$$.cmd
  endlocal & set %2=%var_% & goto :EOF

  @echo off & setlocal enableextensions
  :: The same with GnuWin32 sed and tr (let's call them unxsed and unxtr)
  set myvar_=My Test String!  åöä
  echo %myvar_%
  call :ToUpcaseWithUnxSedTr "%myvar_%" myvar_
  echo %myvar_%
  endlocal & goto :EOF
  ::
  :: ====================================================================
  :ToUpcaseWithUnxSedTr
  setlocal enableextensions
  echo @set var_=%~1^
    |unxsed y/abcdefghijklmnopqrstuvwxyz/ABCDEFGHIJKLMNOPQRSTUVWXYZ/^
    |unxtr \206\204\224 \217\216\231^
    > %temp%\tmp$$$.cmd
    rem      å   ä   ö    Å   Ä   Ö   in octal
  for %%c in (call del) do %%c %temp%\tmp$$$.cmd
  endlocal & set %2=%var_% & goto :EOF

  @echo off & setlocal enableextensions
  ::
  :: The text to be concerved to upper case
  set MyText_=Scripts are fun, or are they?
  ::
  :: Build a Visual Basic Script
  set skip=
  findstr "'%skip%VBS" "%~f0" > "%temp%\tmp$$$.vbs"
  :: Run it with Microsoft Windows Script Host Version 5.6
  cscript //nologo "%temp%\tmp$$$.vbs"
  :: Call the command line script wchich the script host built
  call "tmp$$$.cmd"
  :: Clean up
  for %%f in ("%temp%\tmp$$$.vbs"
              "tmp$$$.cmd") do if exist %%f del %%f
  ::
  :: Demonstrate the result
  echo %MyText_%
  echo %MyTextUp_%
  endlocal & goto :EOF
  '
  'The Visual Basic Script
  Dim MyString, MyStringUp 'VBS
  Set WshShell = WScript.CreateObject("WScript.Shell") 'VBS
  MyString=WshShell.ExpandEnvironmentStrings("%MyText_%") 'VBS
  MyStringUp = UCase(MyString) 'VBS
  WshShell.Run "cmd /c echo @set MyTextUp_=" & MyStringUp & ">tmp$$$.cmd" 'VBS

  @echo off & setlocal enableextensions
  ::
  :: The text to be concerved to upper case
  set MyText_=Scripts are fun, or are they?
  ::
  :: Utilize a Visual Basic Script
  echo Wscript.Echo UCase^("%MyText_%"^)>"%temp%\tmp$$$.vbs"
  type "%temp%\tmp$$$.vbs"
  for /f "tokens=* delims=" %%s in (
    'cscript //nologo "%temp%\tmp$$$.vbs"') do set MyTextUp_=%%s
  ::
  :: Demonstrate the result
  echo %MyText_%
  echo %MyTextUp_%
  endlocal & goto :EOF