Batch renaming works the same way as renaming on the fly does: it uses the same set of switches. A small set of default renaming schemes is available (like Change extension to lowercase) but if you want to have complete control on how to rename the pictures you can choose the Customoption that will let you define your own mask.
In that case click on the arrow button on the right of the new name field to get a list of all the switches available. The switches are gathered into categories to ease their access in the menu. If you are not sure of your mask then check the Preview changes box. When you click OK cam2pc will show you how each image will be renamed and you will have the possibility to press Cancel if the result is not what you intended.
For instance in the "New name" field specify: DSCN%{num:4}.%{EXT}. Choose a number from which to start. Suppose you have the files Paris.jpg, London.TIF and Madrid.Bmp. Then the three files will be respectively renamed to: DSNC0001.JPG, DSCN0002.TIF and DSCN0003.BMP.
The batch renaming feature of cam2pc is very powerful and lets you rename your pictures exactly as you want!