Another battery option that would be a little cheaper, lighter, and easier to use than the optima would be a 12V 33AH VRLA/AGM battery (http://www.interstatebatteries.com/e...archGroup&js=1
) They are deep cycle (which is what you want) they are lighter, and it's $100 less than a optima.
You can go cheaper and run a wet cell deep cycle, like a marine/rv battery but you will have to deal with the mess. They are much cheaper in price though.
But in the end, I would question if you really need a dyno; unless your building motors most club racers don't need one. I don't know of many pro's who do other than a non dyno like a motormaster.