it was for a vent hose.  the hoses were a paper element type and never
lasted very long.   only the westys had this.  something about  venting battery
gases to the outside but kinda pointless IMO. this also has  something to
do with the westys having the screw down battery sheetmetal cover  with foam
gasket.. also, most of which are long gone.

id just plug the hole with a big rubber plug or some aluminum metal duct
tape.

In a message dated 9/24/2014 2:24:07 A.M. Eastern Daylight Time,
raym02@YAHOO.COM writes:

My 1985  Vanagon has a round hole in the right front wheel well. The hole
is about 3  inches in diameter, in the rear part of the wheel well, and leads
to the  battery compartment.