Although I leave my batteries in my RV with the RV plugged in, I do have other batteries that I want to maintain when I and my RV batteries have gone to warmer places.
I use an old 12V power supply, a solar panel voltage regulator and an old analog VOM to maintain my 2 Quad batteries and my lawn mower as well as my daughters 2 batteries for her horse trailer. I was given all of the above items but if I did not have them I would use an automatic battery tender. The voltage regulator will handle up to 48V input and the output is adjustable and I have it set at 13.2V.
Picture taken today, lawn mower and one quad battery not yet on line so only 3 batteries currently connected.
