1987 Johnson/Evinrude CU Outboards 35A thru 55 Service Manual, Page 251Get this manual
3Capacity Test Satisfactory capacity tests can be made only when the battery electrolyte equals or exceeds 1.225 specific gravity at 80 (27 C)4Terminal Voltage Test
Use extreme caution during any load testingImproper procedures could overheat battery and cause electrolyte gassingThis might create an explosive atmosphereaVariable Load High Rate Discharge Tester (Recommended)