1996 Johnson Evinrude "ED" Electric Outboards Service Manual, P/N 507119, Page 22Get this manual
Battery Care Keep the battery charged at all timesCheck the state of charge by making specific gravity readings with battery hydrometerIt is suggested that specific gravity readings be taken and the water level checked every two weeksIf the battery has been standing for 30 days, recharge the battery before using it to ensure reliable serviceCharge battery to the specific gravity recommended by the battery manufacturerCheck the specific gravity of the battery electrolyte with battery hydrometer, preferably one that has built-in thermometer and correction chartNo other method should be used to determine the charge condition of batteryA hydrometer reading is not, curate if water has been recently added, because the water has ac not had chance to mix with the electrolyteThe proper water level should be maintained at all timesIf water is added in freezing weather, the battery must be fully charged at onceOnly distilled water, or water approved for battery use, should be added to the battery to replace water lost through evaporationNever add acid except when acid has been lost by spilling