RRR:
I've gotten the impression that alot of yakers have used watertight boxes to hold/protect the battery and electrical connections from water intrusion. If you catch a wake and water gets on the connections, you could get a short/sparks, etc., and there's not that much room in a yak to get away from the danger. Some have used cheap tupperware from walmart all the way up to $50 or more water tight/proof containers for their batteries. Granted, some of 'em are out in the gulf of mexico, off shore , etc, and I'm assuming you are in calmer waters, but you could still catch a wake from a boat or wave runner, and short out everything. Cheap tuppeware container will keep most if not all of the water off the connections and avoid some bad trips to the water.
GO BIG ORANGE !
I meant to behave, but there were just way too many other options available at the time.