Mike, I'd recommend this battery tender. I have three which i leave on our dually battery truck and our two tractors during the winter. They have worked very well, use minimum energy and keep the batteries fully charged.
Not a fan of amazon but that was first link I found.
https://www.amazon.com/Battery-Tend...47578258&sr=8-1-spons&keywords=021-0128&psc=1
Not a fan of amazon but that was first link I found.
https://www.amazon.com/Battery-Tend...47578258&sr=8-1-spons&keywords=021-0128&psc=1