In a 1st gen MCS next to the battery is a orange type of module. What is it and if I hear it clicking right after a hard start is it normal? Anyone have the Bently manual that might have a diagram showing this?

I have been having a problem in my 2004 MCS with hard starts, and every once in a while the car will just give a loud click and the battery goes from 13 volts to 4. I replaced the battery and the new battery looses a charge with in a few days. It has been hooked up to a battery tender until it is green, but then if not put back on loose its charge and will not start after a few days. Any ideas?

 

That orange module is a pyrotechnic devise used to sever battery power in a bad accident. The clicking strikes me as being unusual...

 

The BST(battery safety terminal) is actually part of the positive battery cable and not in the little yellow box.

The little yellow box(it's not a module, the yellow cover just pops right off) just has high amp fuses in it connecting the two positive cables back there.
The fuses inside it look like this...