As an S-Type owner, you'll be aware (I guess) of how sensitive the electronics is to low battery voltage. You'll maybe not know though, what you're expected to do after dis-connecting and re-connecting the battery.
I've put together a PDF document which takes you through the procedure step by step. Nothing that isn't readily available elsewhere but just gathered together and (in my view) logically ordered into a single reference.
It also includes how to get the audio system working when you don't have the security code
I've been asked for it so many times that I though I'd make a thread just for access to that document so here it is:-
Battery reset.pdf