Digging further to see what else needs doing, I found a battery. But not just any battery!
I removed the white powder (leaking of course). OK, I can understand a two cell stacked battery, but these are obviously different capacities. I think they are Ni-Cad.
Is this custom made? Never seen anything like this...
May have to use an external pack with two cells as clearance to the next board up is very tight.