I experienced this the other day. Thought it was the 180 a fuse. It was, however, a copper lug that had broken. The break was located on the copper lug flat, where it transitions to the circular part. There was evidence of heat, on the insulation. What I found was that all the 5/16" SS bolts were not as tight as when I installed a new pack. I guess the lead cold flowed, over time. Maybe there was some thermal cycling that set this up. I would recommend checking the bolt torque on a battery pack cables periodically. I only had a split lock washer on each bolt.