If I were to do your task, I would have added some steps for clarity and conservatism. You might find your renamed files in whatever folder you were using when you called this bat file.
I think you are trying to same too much typing.
I would have said:
cd c: \folder1 (space only for anti emoticon purposes)
ren *.xls *.csv
cd: \folder2
ren *.xls *.csv
cd: \folder3
ren *.xls *.csv
The above approach makes it absolutely clear where the files you are tampering with are located.
See if this helps.
seacue
Oops...shuttlebus seems to have got there first...