I have a 21 ft. Skeeter with a 36 volt, 101 pound thrust Terrova. I have never pulled cranks with it, as I use my smaller boat for that. My question, is with 3 new group 31 batteries, how long will they run pulling cranks at 1.7 - 1.8 mph? I know that wind plays a role, but on an average fishable day with manageable winds. Thanks.