Mercedes-Benz SL320 Forum : “How to open the boot/trunk to access the battery when battery flat and boot will...”

You should be able to unlock the trunk manually with the key. Turn it to the left to unlock the truck then turn it back to the center and push in. Here is a copy of the owners manual that might help you. http://www.brianclifton.com/Mercedes-Benz/Manuals/R129%201994%20Owners%20Manual.pdf