battery hold down and rear blind mechanism

Hello everyone. I lurked briefly on this terrifically informative site and then bought an 89 500SEL and am getting getting down to some maintenance as the PO wasn't very hands on. First thing was sort out the unholy mess underneath the battery tray. No rodents, just a lot of that white powdery corrosion. The question I have is how many clamps are there to hold the battery down. I only have one there, but it looks like there is a spare hole and place for another one. Should there be two?
I've also pulled out the non-functioning blind mechanism and have fixed it all ready to instal using an old antenna cable from a Saab I had lying around. I've included a shot of it for all those of you who wonder what goes on under the cover. If anyone's interested I could document exactly what I did after I get it al back in and up and running. The only thing I'm not sure of is how much tension to have in the spring retraction mechanism. It sure would have been a lot easier to remove if there was access from the boot to the four nuts that hold that motor and roller blind cover unit on.