====== Convert all files in a directory to lowercase ======
use drag and drop in the Explorer or start the batch manually

<code cmd files2lower.cmd>
@echo off
SETLOCAL ENABLEDELAYEDEXPANSION

set _dir=%~1
if not "%~1"=="" goto checkdir

:ask
  echo.All Files will be converted to lowercase
  set /p _dir=Directory [%_dir%]:
  
:checkdir
  call :cleandir %_dir%
  if "%_dir%"=="" goto ask
  if not exist "%_dir%\." (
    echo.Directory %_dir% not found!
    goto ask
  )

 echo Dir "%_dir%" 
 echo.|set /p x=convert Files to lowercase in progress ...
FOR  %%V IN ("%_dir%\*") DO (
 set _file=%%~nxV
 call :convert_to_lowercase _file
 echo.|set /p x=.
 move "%%~fV" "%%~dpV!_file!"
)
 echo.done
goto end

::functions
:convert_to_lowercase
if not defined %~1 goto :EOF 
for %%a in ("A=a" "B=b" "C=c" "D=d" "E=e" "F=f" "G=g" "H=h" "I=i" "J=j" "K=k" 
            "L=l" "M=m" "N=n" "O=o" "P=p" "Q=q" "R=r" "S=s" "T=t" "U=u" "V=v" 
            "W=w" "X=x" "Y=y" "Z=z" "Ä=ä" "Ö=ö" "Ü=ü"
            ) do call set %~1=%%%~1:%%~a%%
goto :EOF 

:cleandir
  dir /AD "%~1" /b >nul 2>&1 && set _dir=%~1\\\\\|| set _dir=%~dp1\\\\\
  set _dir=%_dir:\\\\\\=%
  set _dir=%_dir:\\\\\=%
  
goto :EOF 
  
:end
  ENDLOCAL
</code>