I have a three bank charger that I leave plugged up year round. After a day of fishing, (daylight to two thirty or so in the spring or fall) the first two years they will recharge in six to eight hours. The third year it may take twelve hours to recharge. I don't pull cranks so it sits idle during the heat of summer. When do most of you change them out and should I unplug when it's out of use for an extended periods. I check the water levels every couple of months.