Mercury Mariner 200, 225 Optimax Outboards Service Manual, 90-855348, Page 72Get this manual
A fully charged battery will have specific gravity reading of approximately 1.270 at an electrolyte temperature of BO (27 C)If electrolyte temperature is above or below BO F, additions or subtractions must be made in order to obtain hydrometer reading corrected to BO standardFor every 10 (3.3 C) above BO F, add specific gravity points (.004) to hydrometer readingExample: hydrometer reading of 1.260 at 110 (43 C) would be 1.272 corrected to BO F, indicating fully charged batteryFor every 10 below BO F, subtract points (.004) from the readingExample: hydrometer reading of 1.272 at (-1BO C) would be 1.240 corrected to BO F, indicating partially charged batterySPECIFIC GRAVITY CELL COMPARISON TEST This test may be used when an instrumental tester is not availableTo perform this test, measure specific gravity of each cell, regardless of state of charge, and interpret results as follows: If specific gravity readings show difference between highest and lowest cell of .050 (50 points) or more, battery is defective and should be replacedELECTROLYTE LEVEL Check electrolyte level in battery regularlyA battery in use in hot weather should be checked more frequently because of more rapid loss of waterIf electrolyte level is found to be low, then distilled water should be added to each cell until liquid level rises approx316" (4.Bmm) over plateDO NOT OVERFILL, because this will cause loss of electrolyte and result in poor performance, short life and excessive corrosion Charging Discharged Battery