If what you mean that your S500 is "taking a while to crank up" by the starter turning over slower then it very well might be your battery not putting the full 13.2V out or your alternator not charging you battery fully.

__________________
Ray
1998 Mercedes E320, 200K Miles
2001 Acura 3.2TL, 178K Miles
1992 Chevy Astro, 205K Miles