Based on a couple of replies I received, here are some additional details:

1.  This is the Passenger Side battery

2.  Swiveling the seat to the side and/or all the way around does not do
the trick.  As I mentioned, the obstacle to getting into the compartment
seems to be the *base* of the seat, which as far as I can tell does not
swivel.  It's the thing that the swiveling parts attach to.

Hope this makes it more clear, & thanks for feedback so far!

Kathy