Batteries Not Included

Yesterday I was waiting for my connection on the A train at 42nd street.  And looking down on the track I expected to see the usual garbage and perhaps a creepy rodent... but instead I saw a bunch of AA batteries.  In the ten foot section in front of me I counted 42.  Where do they come from?  and why do they stay there?  And why AA?  Why not a 9v or two?