1978 Johnson 55 HP Outboards Service Manual, Page 97Get this manual
DESCRIPTION The complete electrical system is made up of the ignition system, the starter system, the alternator charging system, and the storage batteryAlso included are the instrument and cable groupSee Figure 7-1 at end of Section BThis section will cover the starter system and the charging system, and battery maintenance
The sources of deficiencies noted in the visual inspection should be located and corrected before installation of new batteryBHydrometer
This test can only be used when there is sufficient electrolyte above the battery plates to fill the hydrometer tubeDo not, however, take readings immediately after refilling the cells with waterSpecific gravity will vary points (0.004) with every 10F (6C) temperature changeFor each 10F (6C) below BOF (27C) subtract pOints from hydrometer readingFor each 10 (6C) above BOF (27C) add pOints to hydrometer readingAfter correcting to BO (27C), interpret readings as follows: