Seriously consider mounting the extra battery mid boat or forward. The extra weight of the fourth battery has a big impact on my planning from a dead stop. I also sit more heavy in the rear end because of it. Try to distribute the weight better if you can.
LiftSaver Trolling Motor Mounting Bracket - Patent Pendingwww.liftsavertmmount.com
Works with MG Xi5, Xi3 and MK Terrova, Ulterra, PD V2 and Riptides as well.