Last month (8/99) I left the fog lights on and drained the battery. After asking around to find someone with jumper cables who could provide a jump, I opened the hood and didn't find the battery. Feeling stupid I got out the Owner's Manual and looked up battery. It said it was in the back. Opening the hatch and moving the deck cover revealed the spare tire but no battery. I then went back to my office and looked on all the 928 Web sites and found a mention of the battery being located under the spare tire. To help other neophyte 928 owners, here's some pictures. You'll notice I got my own jumper cables now. I also found that there is a remote jump point in the front of the car that can be used without getting to the battery, and as Jerry Schuryk points out is probably safer. Some people use this as a place to mount a trickle charger.
For more information about the 928 battery from Simon and the folks on the Rennlist.
Copyright 1999, George A Suennen