I'm with you during the off season. I cover the boat sometime around Thanksgiving, top off the batteries, unplug them and they are on their own for the next 4-5 months. Wait for the first warm spring day, plug the batteries in and it take about five to ten minutes and the batteries are at full charge. Has worked for me for the last 30+ years.
I jumped to Lithium this year. I'll do the same routine again this year, except with the batteries. I will leave the batteries at about 50-60% SOC over the winter, and not recharge until after the first shakedown trip in the spring.
Can't wait!!!!