Sporty:
My batteries, as delivered from the Kirkham Wizardworks, are Werker WKA12-33J, 12V, 33Ah. Dimensions are 7 5/8" H, 5" W, 6" H. Obviously, the tray is 15 1/4" by 5".
Here's a link:
http://72.14.253.104/search?q=cache:...&cd=1&ie=UTF-8
You might also try to order them from the Kirkhams.
Salty