Should I leave the MH plug in all winter?

I have three of These. I leave them plugged in all the time that the MH and Toad sit in my building. House battery in the RV and engine batteries in both. They detect the existing battery charge, charge at full capacity until fully charged and then drop down automatically to a maintenance level. I've been using the same batteries for ten years without having to replace any or add water.
I found them at my local Batteries Plus store.