1988 Johnson Evinrude "CC" 9.9 thru 30 Service Manual, P/N 507660, Page 309Get this manual
3 Capacity Test Satisfactory capacity tests can be made only when the battery electrolyte equals or exceeds 1.225 specific gravity at 80 (2r C)[]] Terminal 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) Connect tester to battery terminal postsDischarge at rate of three times battery ampere hour rating for 15 secondsIf the voltage is .6 volts or higher at the end of 15 seconds, the battery has good output capacityb .FixedHesistanceTester