I'll keep the battery voltage problem in mind. I usually try to insure that my batteries are not getting too low before I put the boat in the water again. I use LiFe batteries, and they hold their voltage until the point where they are almost completely discharged. That's good to maximize the power that they can deliver, but not so good if you are far out on the water and they start to go flat. I usually time my excursions so that I have a good idea that the battery still has plenty of juice left when I'm bringing it back to shore. My boats are all smaller and probably don't draw more than an amp when at full throttle, so the batteries last a long time before needing a recharge.
Bob