Others here have reported good luck with old fork lift batteries in RE systems. My only experience with them comes from the warehouse where I lease and manage a camera system to them. They charge the thing off of a charger which works off of a timer, and routinely over charge it, and also routinely allow it to deeply discharge. Still, the battery seems to to just keep ticking along. I know that they use a different Lead-Antimony alloy in the plates. They seem to tolerate a lot of abuse compared to most batteries. Still, if you are getting a used one, its value would be determined by its actual design, capacity and condition. Some businesses will likely keep their units in service until they no longer function. If they recondition it by adding some kind of snake oil or EDTA, that may not be worth much. Rich