Hello @kees66. I haven't seen a metal battery box in a P6 before. Not much left of that one, anyway! I've had a couple of these cars and mine always had a battery box and lid made out of some sort of hard black plastic.
While you are fixing your power steering, I think you will probably need one new hose. In your third photo above the hose looks as if it is leaking, and an attempt has been made to repair it with some red tape, and a hose clamp. I am not really familiar with the power steering hoses on left hand drive P6s, but I think this is the high pressure hose from the pump to the steering box. So I doubt it is really possible to patch up a leak anywhere along that hose. I took my old steering hoses to a hydraulic repair company who mostly worked on dump trucks, bulldozers, cranes and the like. They had no trouble replicating it.
It has a plastic layer over the metal, maybe that is also with yours, a magnet will give answer.