1971 Johnson 40HP outboards Service Manual, Page 68Get 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 If batteries are to be fully charged by means of a
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 timesIf water is added in freezing weather, the battery 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 securely fastened to the boatA loose battery may shift in the boat, damaging itself or other eqUipment