1998 Johnson Evinrude "EC" 9.9 thru 30 HP 2-Cylinder Outboards Service Manual, Page 280Get this manual
Battery Specifications
For each motor, provide one battery that is: 12-volt, heavy-duty, designated "marine" Ventedrefillable or maintenance-free Rated 360 CCA (465 MCA) with 90 minutes reserve or 50 amp-hr
Deep-cycle batteries are suitable IF they meet or exceed the minimum CCA requirements
Installing and Connecting Batteries and Cables
Place the battery so it is easily accessible for frequent checking and recharging and in hold-down systemInstall positive cable to positive post and negative cable to negative post
When connecting to the battery, begin by placing largesurface starwasher over the threaded battery post, then stack cables from accessories, then cables from the motorFinish the connection with hex nut, tightened firmly with wrenchwere supplied with the batteryWing nuts can loosen and cause errant warning horn signals or electrical system damageApply OMC Electrical Grease to connections