Kind of depends. Do you have flooded battery(s) or AGM? Old, dumb converter-charger or one of the modern smart chargers with bulk, absorption, & float?
Plenty of warnings in the mainstream RV forums about how the old dumb converters can boil all the water out of batteries if left plugged in all winter
Probably safest to bring it up to 100% charge and pull the ground cable off it. Maybe halfway through the winter put the cable back on and plug it in for the weekend, then pull the cable again.
There are various things like CO and Propane leak alarms that can kill your battery and let it freeze. Some of these BYPASS any battery off-on switches on some RVs so they stay on all the time. Hence pulling the cable.
A smart converter – as long as it’s working right – shouldn’t hurt the battery(s) if left plugged in all winter.
Regards
John
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