1998 Johnson Evinrude "EC" 90, 115 SPL Service Manual, P/N 520209, Page 226Get 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 ft(6,1 m), regardless of cable diameter
These specifications do not apply to aluminum battery cablesOMC does not recommend the use of aluminum battery cables