1991 Yamaha Outboard Factory Service Manual 9.9 and 15 HP, Page 113Get this manual
BATTERY If the battery shows the following defects, it should be replaced1The battery voltage will not rise to specific value nor will bubbles rise in any cell, even after many hours of charging2Sulfation of one or more cells occurs, as indicated by the plates turning white or an accumulation of material in the bottom of the cell3Specific gravity readings after long, slow charge indicate one cell to be lower than any of the others4Warpage or bucking of plates or insulators is evidentWARNING: Battery fluid is poisonous and dangerous, causing severe burns, etcIt contains sulfuric acidAvoid contact with the skin, eyes, or clothingAntidote: EXTERNALFlush with waterINTERNALDrink large quantities of water or milkFollow with milk of magnesia, beaten eggs or vegetable oilCall physician immediatelyEyes: Flush with water for 15 mimutes and get prompt medical attentionBatteries produce explosive gasesKeep sparks, flames, cigarettes, etcawayVentilate when charging or using in an enclosed spaceAlways shield your eyes when working near batteryKEEPOUTOF THE REACH OF CHILDREN The service life of battery is usually two to three yearsLack of care, as described below, will shorten the life of the battery