1992 Johnson Evinrude "EN" Electric Outboards Service Manual, P/N 508140, Page 74Get this manual
General Safety Warnings
Do not charge battery in the boat with an external chargerFumes vented during charging can lead to an explosionBefore working on or removing any electrical parts, disconnect the battery cables from battery to prevent electrical sparksIf external heat is required to service any component, allow the component to cool to the touch before continuing service