I use a batterytender for my father's explorer. It comes with both the alligator clips and ring terminals for permanent install of the wires.
There is a connector so that you can remove the charger when not needed.
My father stopped driving several years ago, so this is a spare car when my sisters visit. I keep the battery minder on for the couple of months between visits.
https://amazon.com/gp/product/B000CITK8S/ref=oh_aui_search_detailpage?ie=UTF8&psc=1