I’ve always heard a slower charge is better FWIW. That and are you that much of a fishing animal to need to charge things that quickly? I only have a 12 volt system for my trolling motor, and only a 6 amp charger, but have never had problems having enough charge for one day, and having it recharged for the next, even when a rare day comes around that I actually kill most of the juice in my trolling battery. I would bet the 6 is fine, and even if it wasn’t enough, and assuming you gotta trailer the boat a bit, I’d get one of the trailering charger, so you can charge the batteries on the way to the lake, for the around the same amount of money you’d spend on the bigger charger.