The PCB just inside the battery terminals is a little scorched. I think a lot of the heat was emanating from this area and tracking down the busbar. Some of the screws around here were a bit loose, so I've nipped them all up.
Some pics attached for the curious. I'll probably look at replacing the positive cable sheath as it looks a bit scruffy and there's not much protection against being touched at the moment. Sanded down the positive terminal as well, looks nice and clean again now.
