Try Irfanview - a pretty nice image viewer. Install the plug-ins as well so that you can directly view RAW files. There is a batch function for either renaming only or also image processing.
But basically you don't need a program, some shell (command line) knowledge helps to do this.
It adds a context menu item to your right mouse click. Amazing list of options to batch filename / replace names, and no learning curve to speak of. The software wasn't free then though (don't think it still is now).