Matt,
One thing you might want to consider is buying an onboard charger that will go into the "float" mode once the batteries are charged. This way you won't overcharge your batteries and ruin them. Check BPS or Cabela's they have several to choose from. I bought the Bassmaster 2 bank, 20 amp charger last year and it works great. You just plug it in and leave it alone until you're ready to go fishing. One other feature it charges your batteries very fast, I believe it will charge a depleted battery in less than 4 hours.