Depends what year it is --> 996 Monoposto, Biposto, S 01-02 YT12B-BS
or 996, S, SPS 99-00 YB16AL-A2 which is what was in mine (MY 2000)
I replaced mine with an Odyssey PC 680 which is more expensive, has more cranking capacity etc but doesn't fit the standard battery tray - it's around 4mm wider than the YB16AL-A2.
If you want to go down the PC 680 route then U2U Iconic944ss as he has that I think he doesn't need (was going to sell it to me)
Read this thread -
http://217.199.188.40/xmb/viewthread.php?tid=9071 TP