When I open the hatch on the rear of my 71 bus, I note the battery on the right side of the compartment.
There's nothing on the opposite side. However, the floor of the compartment has stamped grooves or indentations that look like they were meant to fit some thing that is no longer there.
Did VW ship these buses with, oh, I don't know -- a jerry can or parachute brake or lunch box or something mounted over there?