I use a Noco 2D on my F150 which only get drive every couple of months. And I got the direct connect for a better connection. It mounts under the hood and I just need to plug it in.This is what I've been using to trickle charge my riding mower batteries, and I've been very pleased with it.
Amazon.com: Battery Tender Junior 12V, 750mA Charger and Maintainer: Automatic 12V Powersports for Motorcycle, ATVs, and More - Smarter Than a Trickle Charger - 021-0123 : Automotive
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I just noticed that it calls itself a "Junior" charger, and it says it's for motorcycles and ATV's. I'm guessing that it's too small for a tractor?
NOCO Genius 2D