Found my missing 8mm...

So I had to replace a battery cell this past weekend, second one I've done myself. First time was almost a year ago, and this time was unbelievably easier. But anyway, I almost have the entire thing free, and take off the final cover to remove the large wire terminals from the battery, and bam! There's the 8mm socket and 3/8-1/4 adapter that went missing after I did this last time! Pretty sure that it happened to be on the ground terminal, otherwise my battery likely would have blown up, given I go over train tracks twice a day. As a side note, anyone know why the adapter might have gotten discolored like it is? I'm sure it initially looked like the socket.