Once I went to 31 series Diehard Platinum AGMs, 3 batteries will last a whole day on a no-motor lake with livewells and graphs running all day, and still have plenty of power to crank the motor at the end of the day. Personally, I dont want the weight of the extra battery if I dont need it. Plus, if you run the motor at all during the day it recharges the main battery as you run.