The one I used was the standard Optima blue top, think it was a 34m. It fit, just barely, in my E22 so it should fit.
Derek, do you sprinkle it with fairy dust or what?? Never had a battery last more than three seasons. I'm back to conventional, group 58 in the starting batt hole and a group 24 deep cel with same old Hellroaring isolator in between. Just running amplifiers:) My new neighbors hate me already;)