I use a 12v deer feeder battery for the FF on my yak, can get 'em at Academy sports/Gander Mtn and the correct charger for $30-40. then build a battery box with a $5 dry box from walmart, some quick connect electrical connectors for the wiring, some goop, and it's dependable, rugged, easily removed for transport and installes in 30 seconds at the ramp. These batteries will run a simple FF (Lowrance Mark 5 pro) for 4+ trips of 4+ hours/trip.