1990 Johnson Evinrude "ES" 9.9 thru 30 Service Manual, P/N 507871, Page 278Get this manual
1Visual Inspection The first step in determining the condition of battery should be visual inspectionLook for conditions such as damage to the case, loose terminals, evidence of electrolyte seepage, etcThese signs may indicate improper care, installation or application of the battery Look for excessive corrosion on the battery terminals and cables Check the battery cables for worn or frayed insulation Replace cables, if necessaryCheck the electrolyte level in each cellIf electrolyte level is below the plates it is possible the battery is permanently damagedAlso look for dirt, oil or other contaminants floating in the electrolyte[Hydrometer
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INote Disconnect