Well, I knew the battery was under the backseat.
But, I never actually looked until today.
It sounds like this is true for 2000-2005 Bonnevilles
I didn't see any pictures on this website after a search....
Anyway, while I had my camera out for my little blower fan problem...
I snapped a few pictures for the rest of us that never looked under the seat before.
The back seat is easy to remove. It'* very light. Do not be afraid.
It'* held down by a couple spring clips. Just pull upwards on the front of the back seat.
And under the seat... yes! You've read about it! You've dreamed about it! The battery! and most of the interior fuses.
The fuse cover is removed by squeezing the clips on each side inwards. (same as the fuse box under the hood.)
There'* a nice chart under the cover. Be warned, the chart seemed to be "upside down" for me.
There'* a fuse puller in there and spare fuses.
Sorry for any errors. Feel free to correct and comment.