I don't know what the number is but have had an Optima "blue top" in mine for almost 10 years with never a falter. You fcan measure the dimensions if that's an issue. I didn't know Optima made anything but the three colored top models red, yellow, and blue. You should be able to get two blue tops in one side without any problem. It's my battery of choice, since I have had this one for longer than any other battery I have used in my boat, for 30 years of boating, by far.
