What is this small tube? [pic inside]

[danielfb]

I tried to replace the battery and found this tube hanging around in the battery compartment.
Any clue about what is it?

 

[t-tony]

Some batteries have a breather tube which allow any gases released by the battery to vent outside of the car boot. Not all batteries have them.

Tony.

 

[TriumphZ3]

As Tony says it's a breather tube. Look around the top edge of the battery, there may be a small hole that it fits into in one of the side faces near the top..