It looks as though someone took a torch to the cable end & softened the lead until the bolt could be pulled out.
I've dealt with batteries which have been connected for four or more years instead of a paltry four months, and never have I had to get destructive. Once in a blue moon I've needed a long lever, but...
Unless there are a few important pieces missing from your story, I think that whomever did that hatchet job owes you a new battery.