Why? Charging them up at the start of layup and disconnecting them (ie doing nothing) works fine and in the Spring the batteries are at 90+% SOC.So, by all means question which gizmo works best or properly, but any one of them should beat nothing at all.
I do have the test equipment, about $5000.00 worth, I am also one of the only marine electrical systems techs offering physical capacity testing. I am one of the few who has ponied up for the equipment to do that."Why?"
Because you can't SEE the damage and the odds are you don't have access to the equipment to do any real meaningful SOC testing.
And because you don't have the equipment you believe them, then connect to a charger and leave it there thinking it will do good. Remember these are the folks trying to sell you lead who are telling you to leave a battery on constant charge....And yet, they ALL will say what I just said. Thirty days, and you've probably damaged the batteries. 90 days, and you've definitely damaged the batteries.
I had a set of 12 year old GEL's on my bench two weeks ago for capacity testing. They have been on-board for 12 years and not charged in the off season... I have many customers well beyond 8 years with typical wet cells all stored on-board & disconnected. As long as the batteries are put away properly the only real effect you have is stratification but a constant float charger will not prevent that either. Oh the marketers will have you believe their charger is as smart as Einstein they do still do not prevent stratification.It is is pure hog wash that a constant float voltage prevents stratification. You need to roll the electrolyte to do that and this requires voltages above gassing... So now you have stratification WITH additional charge current. Think about it, I do, and this is one of many reasons I will not leave a battery in cold storage on constant float.....You think doing nothing works well enough? OK, do nothing. They'll be happy to sell you new batteries every three years instead of every six or eight years.
Your facts are simply opinion when it comes to winter storage.Not my opinion. Objective fact, repeated and confirmed by every business that's in the business of making batteries.