That's a insulation pad barrier for the battery so it don't rub on the metal boxWhat in the hell is the world coming to? I wouldn't expect this to be a top-notch design, but maybe there's a history here? Is this to replicate what it was like on a 1951?
You don't want that battery bouncing around in the metal box do ya
I cut some outta Felpro rubber/fiber gasket material and glued it on all 5 surfaces inside the box,