I get this question often & since I am working on a 89 Advance this week replacing the starter system I figured I would post the correct battery size for the Advance models with the in-floor molded battery tray/recess. (1987-91) Group 78 is the correct battery for this model, not the smaller group 75. These are side post automotive NOT Marine specific batteries and will have plenty of clearance between the top and the seat bottom, other top post batteries have clearance issues.