I am awaiting delivery of a Terrova 80# with i-pilot. I have an 18' boat also. You can stay on the water much longer with the bigger motor, it doesn't have to work as hard therefore increasing run time on a single charge. I have a 70# fc motor now and have trolled two days without a charge. I know people with smaller 12v motors who can't troll over 6 hours on a charge.