1993 Johnson Evinrude "ET" Electric Outboards Service Manual, P/N 508280, Page 21Get this manual
2Hydrometer Test This test can only be performed when there is sufficient electrolyte above the battery plates to fill the hydrometerIf electrolyte is too low, add water until level is correct Do not take readings immediately after adding waterRecharge battery to mix acid in water before testing INote Disconnect battery cables before charging battery[] View the hydrometer with your eye on the same level as the liquid surfaceThe float of the hydrometer must float freely and not stick to the sidesMake correction for the battery temperatureSpecific gravity will vary points (0.004) with every 10F (6C) temperature changeFor each 10F (6C) below 80F (2JOC)' subtract points from hydrometer readingFor each 10F (6C) above 80F (27C), add points to hydrometer readingAfter correcting to 80F (2JOC)interpret readings as follows: All cell readings the same at 1.250-1.260 specific gravity indicates battery is good and fully charged All cell readings uniform and below 1.225 specific gravity, recharge fully and retest Variation of more than 30 points (0.030) specific gravity between any two cells, indicates battery condition is questionableRecharge and retestReplace battery if variation remains after recharging