A couple years ago I bought 4ea 8G8D 12VDC batteries. I wired them in series and put them in a remote pump house to run a well pump. Not long after they were installed, one failed. I turned off the well and they sat on a solar charger set for GEL batteries. I am replacing the batteries with AGM batteries. It looks like 3 of the batteries are still good with little use. I am offering them for sale at $200.00 ea for an $800 new priced battery. If you want them PM me. transportation at your cost.
By the way $200 is pretty much the core charge.