Quoth Andrew B.
You're actually missing one.
I actually found 25, but not all of them were "Batman".
Here are the other 13, which was the missing one:
Paul Ruebens - Robot Chicken
Eric O'Keefe - Nightwing: Escalation
Dave Franco - Young Justice
Benjamin Ciaramello - The Riddler vs. Harley Quinn: A Love Story
Mikey Day - Mad
Nicolas Lee-Demetrius Korokidas - The Joker Blogs
Ken Smith - Mr. J
Zeb Wells - Robot Chicken
Patrick Warburton - Robot Chicken
Gabriel Sabloff - Grayson
Brett Rickaby - Return to the Batcave: The Misadventures of Adam and Burt
Michael Bell - Superfriends
Shannon McCormick - DC Universe Online