Gator, based on what I was told by my battery manufacturer, EVERY boat owner needs a charger. After talking to the folks at Yamaha, I fully agree.
After taking your boat out, even if you turn everything off when you reach the dock, the motor will not leave your batteries at a FULL charge. For sure if you leave anything hooked up as you travel home, the batteries will continue to discharge.
Yamaha and Lifeline Batteries both said to put the boat away with the batteries fully charged if we want them to last longer. I have chosen to follow their advice. Why purchase batteries more often? I can use my money better than they can. I even hook up the charger for a few hours if the boat is not out in two weeks, and always charge them the night before going out.
Just my opinion.
Lifeline Batteries - Marine & RV Deep Cycle Batteries