1999 "EE" 90, 115 FFI, 150, 175 V4, V6 FFI Outboards Service Manual, P/N 787024, Page 147Get this manual
Auxiliary Battery
INote Disconnect all accessories from the auxiliary batteryAuxiliary battery must read minimum of volts at the beginning ofthese testsThe auxiliary battery must remain connected to the outboard during the tests1Check battery ground cable for continuity
2With key OFF, check battery voltage at auxiliary battery, then check voltage at auxiliary battery connection If the readings are not the same, replace wire to auxiliary batteryThe auxiliary battery wire must be at least 10 gauge and it must be protected by 50 amp fuse or circuit breaker at the battery
3With engine running at 1000 RPM, voltage must read higher than in Step and increase steadily to approximately 14112 volts as the engine RPM increases