I'm afraid I don't. I actually haven't had one for like 2 years. And I just put it in the battery bin at the local dump. I now know that there will be a core charge. Just when I accepted planning to pay 160$ for each of the interstate GC battery I chose, I learned that I had to suck it up and pay 25$ more a piece... Oh well.
And that's good to know about the core exchange. I live at a park where it's more likely than average to find someone willing to give away an old battery.
But I can't complain about the money, because I do have it available, I just would rather not spend so much. And being able to have lights and possibly other things like fridge everywhere I go, even at truck stops on the way is a very exciting prospect worth money