I use a single battery tender at home and bought a 30' extender for the charging end, each battery I charge has the quick connect on it so it is easy to rotate. I charge 4 batteries at home this way, takes each battery a day or so to come up to charge, do it once a month.
I helped set up a new sporting clays course at the local Boy Scout here camp 2 years ago - we had to figure out how to keep 30 automotive batteries charged for the throwers. We bought 3 of these 10 bank charging stations and they work great.
https://www.amazon.com/Battery-Tende.../dp/B000NCOKVU