1998 Johnson Evinrude "EC" 25, 35 HP 3-Cylinder Outboards Service Manual, Page 216Get this manual
Battery Cable Extension The following are MINIMUM specifications for stranded copper cable without splicesCable measurements given are from the motor to the batteryThe maximum length is 20 feet, regardless of cable diameter
These specifications do not apply to aluminum battery cablesOVIC does not recommend the use of aluminum battery cablesMinimum Recommended Gauge