Trickle charger/maintainer for the winter.

Looking to buy a trickle charger for my ATV.  The winch/plow really draws the battery down, and if we have deep snow to push it gets questionable whether I have enough juice to finish plowing.

Looking for a model that has the little pigtail with ring terminals to make it simple to plug it in between plowings.

Any brands/models recommended?  Any to avoid?

Also, why is it so dang hard to find red ring terminals in stores?  I want to cut the alligator clamps off and put rings on so I can put that pigtail on my cycle.  Red connects to positive - why do stores sell blue and yellow?

PS - I bought a cheap trickle charger (Black and Decker) that has options for Cable Clamps or O Rings. The connector with the O-Rings is only a few inches long so I leave it attached to battery at all time. It allows easy/quick access and connection with the actual charger.

Colors are for wire size.  Just get some red electrical tape to mark the positive side.