2 years ago I purchased a battery charger, batteryminder 12248, that will charge, desulfate and then trickle charge as needed. It has yet to damage a battery. It is always connected to a battery. Once it's done desulfating one battery, I move it to another battery. I have over 20 batteries, half of which are mower batteries, some tractors, cars, truck, 2 marine. My oldest battery is 7 years old. I haven't bought a new battery since I bought the charger, 2 years. In the past I was buying 2-4 batteries a year. I also bought a battery conductivity tester. It shows all my batteries are in good health.
My advice is buy yourself a Christmas present. I would highly recommend a charger like I got. Then you won't have to worry about damaging a battery, which I've done with the old school manual chargers.