Bob is correct about the vent line.

The funny thing is that hydrogen is lighter than air. Thus when the tube goes from the battery and then down it acts like a reverse sink trap and allows the hydrogen to accumulate at the high point in the tube. The problems begin when the hydrogen builds up in a high point FYI like the inside roof of a vehicle, building etc. thus the battery box in my boat has small holes in the cover so the hydrogen can escape. -- According to NFPA the safe limit for hydrogen in air is 5% (but real experience says that 7-8% is OK).

An Audi with the battery under the hood is safe without the tube because there is plenty of space around the hood for the hydrogen to escape and an Audi with a battery under the rear seat has the same safety feature because of the leaky sunroof.

BTW the Hindenberg did not explode because of hydrogen. It was the highly flammable metalized coating that the Germans used to seal the blimp. It was almost like gun powder!

 

so it was indeed the first hunch.

NH, as I was reading your post, two similar tubes/hoses (however, those are all-black) came to my mind instantly. I noticed them on both sides of the sunroof tracks.

Bob, NH, you guys are priceless® ! Thanks much.

 

These are for water drainage.

 

I don't think we talk about the same hoses, Zippy.
You can actually see the drainage hoses in my other thread, "Sunroof Leak", where I posted pics of them, all 4.

I am talking about a small hose that's on both sides of the sunroof housing tracks, and are sort of "riveted" in place. I will take pics to show exactly what I'm talking about. Those two have an open end.

 

open-end detail