I have a different point of view on battery maintenance for the winter. The 3-state chargers are certainly an improvement over the older chargers but they are not smart chargers; it is a trickle charger. You can't leave even a trickle charger on a battery indefinitely as it will ultimately "boil" the water out and your battery will be over-charged. IMO, a better strategy is to unhook the battery from the trailer and hook it to a smart maintainer; like a Battery Minder. It is smarter than the 3-stage converter and it also has anti-sulfation technology. I've used this kind of product for years with great success. My batteries last me for years. My motorcycle battery finally needs replacement but it is 10 years old; maintained by a Battery Minder.
If you do leave the battery hooked to the 3-stage converter, I would make sure to regularly visit the battery (ies) to check the electrolyte level. You can use this strategy but you can't just walk away until spring IMO.
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