I’m not a fan of keeping batteries on a trickle-charge for long periods.. it’s just one of those things. As a previous poster suggested, the best thing for them is to exercise them once in a while..

Hook up a good load, like a 60W car head light, and run it ’till the light starts to dim. Then put it on a 2A charge for a day and leave it for a couple months.. then repeat. If you can keep it slightly warm (like, 40-50F) that is ideal.

But some of them, despite the best care, just die early.. for any number of reasons. I’ve heard the "not on concrete" thing before, but I don’t know why it’s said or if it’s valid.