I left one attached perhaps half the time through a winter on a tractor that was only used occasionally. It boiled out far more water than I expected. I found the water level down exposing the plates 2~3 times during the winter.
Now I use it only as a charger, left on for a couple of days, and only after I see that battery voltage is below 12.5 volts.
These don't have any shutoff. They are supposed to reduce current as the voltage rises - but I'm not convinced they do.
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I like the idea that I saw in a prior thread, mounting a cigarette lighter socket as a charging point and also to draw power for a sprayer. Be sure to include a fuse in that circuit! I darn near burned up the tractor and the tree I stopped under when I turned the watering trailer too sharp, and crimped the wire going back to the trailer. I didn't think lightweight clips on the battery, same cheap clips as that charger, could draw enough current to burn 18 ga lamp cord. Wrong. Luckily I was wearing gloves and got the clamp off the battery before I burned up more than just that cable. My watering circuit is now fused!
