Change letters into using batch

Change letters into using batch

I'm trying to create a batch file that will change some input text and
change them into their number counterparts of a=1,b=2,c=3 etc for example:
@echo off
set /p text=
echo :: %text% :: echo Is this correct? pause cls
for /f delims=: %%i in (%text%) do ( [something that changes the letters
into numbers] )
Thanks in advanced