Couple of thoughts
One is:  I turn seat around 180 degrees and slide seat back (toward
front of vehicle.)
Another is: there may be a clamp which holds the base of the battery.
Look in the spaces fore and aft of the battery. You may see a 13 mm bolt
and a metal plate.  This clamps a flange on the bottom of the battery.

John Jensen, Mudbug Pottery
mudbug@toadhouse.com , http://www.toadhouse.com