What is this black rubber tube connecting to 12V batter?
 

2007 Nissan Altima Hybrid, purchased in 12/2007.
I think it is about time to replace the 12 volt battery, thus last week I ordered an Optima yellow top battery, as I was replacing the orig Panasonic 12 Volt lead acid battery today, I found a black rubber tube connecting from the side (toward the top of the battery), not to far from the positive terminal (see pic), the other end goes thru the bottom wall near where the battery sit on.

Does anyone know what it is?
I'm thinking it is for the water evaporate from the battery goes thru the tube and goes out of the car, but I'm not sure, I have not seen any 12 volt battery like this.

I'm not sure if I want to replace the battery now, while thinking I'm charging the orig Panasonic battery with my slow charger, it still looks good and holding charge.


Any input?

Update 1 - the black hose is a battery ventilation tube
the Optima D35 is NOT an exact fit replacement,
the terminals are on wrong side, the height is too short, in another word you can't use it without some modifications.
Here is the size of the panasonic battery 6 1/2 * 10 1/2 * 8 (aprx)

Update 2
The optima battery does come with a spacer (at first I thought it was a fancy lid), the battery can sit on it and gain about an inch.
I finally put the optima battery in (sitting on the spacer).

Note: after you replace the battery the "VDC" (on instrument panel) light up, drive around couple of block will turn it off.

Re: What is this black rubber tube connecting to 12V batter?
 

I believe it's a vent tube in the event of hydrogen that might need to be released.

See http://www.elearnaid.com/12vo1topraub.html. I replaced the stock 12 volt AGM battery in my 06 Prius (same battery for 04 to current Priuses, AFAIK) w/an Optima Yellow Top from elearnaid.

Google for agm site:priuschat.com vent tube.