[Foreigner]

Попробуй так

Код:

@echo off
setlocal

set "ni=10"

for %%i in (tst*.dat) do call:ren %%i
goto:eof

:ren
set "fname=%~n1"
set /a val=%fname:tst=1%+%ni%
ren %1 tst%val:~1,9%%~x1