I just noticed this for the first time when I went to remove my battery. Is this supposed to be plugged in somewhere? Or is it some sort of ventilation tube?

 

Im pretty sure mine is the same way except i dont have the L shaped plastic bit

 

Found a quick pic online.

 

that tube plugs into your battery. these batteries are usually vented. well the one i bought the car with was vented and the new one i bought at walmart was also vented.


also i guess the battery can explode if not vented so yeah make sure you vent it. not good to have things exploding right on top of your gas tank

 

hose plugs into your batttery.
check if you have the vented hole in front next to the fuse box or the other side next to the tail light?
if the hole is vented on the wrong side of the battery you need a longer hose to plug into your battery.

watch out for acid leaks from battery, battery under tray will corrode looking like poop.
there are spezial battery carpets absorbing acid you can place under the battery.

I think DRBC43 had some nasty leak from a battery on his under tray many years ago.

 

Yup, found mine was disconnected when I purchased my 43 and the acid vapours had created havoc around the tray. I cleaned as best as I could and rinsed with lots of hot water. Left to dry over a couple of days and applied several coats of Hammerite silver paint. Some corrosion left and probably would be solved by replacing and welding in a new tray.
Make sure the tube is connected at all times and when changing battery ensure it has the breather outlet.