1975 Evinrude 40 HP Outboards Service Manual, PN 5093, Page 76Get this manual
BATTERY CHARGING Boost charge 12-volt batteries at 50 amperes for 20 minutes (1000 ampere minutes)If the charger will not give this rate, charge for an equal number of ampere minutes at best rate availableDO NOT boost battery more than this amount for the "light load test by means of quick charger, the charge rate must be "tapered" (reduced to safe limit) when the electrolyte temperature reaches 125 or when gassing becomes excessiveFailure to do so may harm the batteryIf the battery is to be slow charged, adjust electroIf batteries are to be fully
The specific gravity of the battery electrolyte should be checked with battery hydrometer, preferably one that has built-in thermometer and correction chartNo other method should be used to determine the charge condition of batteryNote also that hydrometer reading is not accurate if water has been recently added, due to the fact that the water has not had chance to mix with the electrolyteThe proper water level should be maintained at all times If wate is added in freezing weathe r, the batte ry should be charged to full charge at onceOnly pure 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 spillingFor mounting the battery, use battery box ecurely fastened to the boatA loose battery may shift in the boat, damaging itself or other equipmentTighten hold-down nuts evenly until battery is secureIf hold-down nuts are too tight, distortion and damage to battery case will result