1990 Johnson Evinrude "ES" Electric Trollers Service Manual, P/N 507869, Page 32Get this manual
Testing Procedures Battery All information necessary to evaluate the condition of the battery(s) and boat wiring is contained in Section 1, General InformationNote Provide separate batteries for the electric outboardIf 1224 volt electric outboard and gasoline outboard must share two batteries, the gasoline outboard must be connected to the No.2 battery to avoid severe damage caused by galvanic corro sion Refer to Battery Connections, Page 1-17Circuit BreakerHand Control Models To avoid damaging components or troubleshooting equipment, disconnect the battery cables before proceed ing ]