@echo off
setlocal &REM enabledelayedexpansion
for %%a in (*) do (
  set "ext_%%~xa=*%%~xa"
)
for /f "tokens=2 delims==" %%a in ('set ext_') do (
  for /f "tokens=1,3" %%b in ('dir /-c %%a^|findstr /e "Bytes"') do echo %%a:  Files:%%b  Size: %%c
)

15 Datei(en),         42291 Bytes               <<< this is the needed line
           0 Verzeichnis(se), 358679015424 Bytes frei