I store my boat and RV batteries in my 60 degree garage all winter with no charger. They are always fine in the spring. The last set of boat batteries lasted 7 years.
I install off grid solar systems in cabins and homes for a living. I install lots of batteries on concrete. I heard that saying about concrete so many times I had to look it up. It turns out that many years ago it was true. Battery cases used to be made of glass and then rubber. Also, concrete had some ingredients in it that could cause a problem. Concrete isn't made that way anymore and battery cases are now plastic. So, while it used to matter many years ago it doesn't anymore. For some reason the myth continues.
I have known batteries to be permanently installed directly on concrete for years and give very good service. Mine sit on concrete all winter. It just doesn't matter anymore.
Look it up like I did.