Yamaha 115-225 HP Outboards Service Manual, Page 54Get this manual
4) Battery replacement is recommended if; 1The terminal voltage of the fully recharged battery will not reach 13.2V2The specific gravity of the electrolyte of the fully charged battery is less than 1.263The battery tester indicates "Unacceptable" area4Specific gravity of the electrolyte in cell is lower than that of the other cells after recharging5) Thoroughly clean the battery terminals, and tightly connect the leads to the terminals, positive cable firstLightly grease the terminals and connectors with petroleum jelly PERIODIC SERVICE
AWARNING
Battery electrolyte contains sulphuric acid which is poisonous and corrosive, i.e it can cause skin bums and damage to eyes_ Avoid all contact with the skin, eyes, or clothingFirst Aid: Eyes: flush with water for fifteen minutes (if necessary holding the eye open with clean fingers), and get prompt medical attentionInternal: Do not make the casualty vomitGive plenty of water to dilute the acidAdd if possible, tablespoons of chalk, milk of magnesia, plaster or whitewash to pint of waterSkin burns: Thoroughly flood the part with waterRemove contaminated clothingBathe the part in an alkaline solution such as two teaspoons of baking soda (bicarbonate of soda) or washing soda (carbonate of soda) to one pint of warm waterBatteries produce explosive gasesKeep sparks and flames awayDo not smoke where batteries are charged or stored_ Ventilate the area when charging or using batteries in any enclose spaceKEEP BATTERIES AND ELECTROLYTE OUT OF THE REACH OF CHILDRENU