Battery Vent - Important


Well, first thing I found out when I went to check Harlem out after her return is that her battery was totally dead. Turns out it is three years old, so it was time for it to die anyway, despite her long “hibernation”.

When I went to put the new battery in, I noticed that it came with a tiny instruction sheet on it re: the use of vent tube, if applicable. The instructions mentioned that the positive terminal cover piece came with a tiny break-away plastic piece that can be used to plug the vent hole on the battery. After that, the instructions make no sense and seem to be self-contradictory (printed in China, maybe?). On the one hand, it indicates that the vent hose from the car is to be inserted into the vent port on the end of the battery, which makes sense. But then, for “safety purposes”, it seems to say use the plug to plug the vent hole in the battery. So which is it? :confused: In reality, if there is a plastic fitting that is supposed to be on the end of my vent hose to attach it to a vent port, it is missing. So, it cannot be attached to the vent hole on the battery. I therefore, thinking the “safety” is the possibility that hydrogen gas might escape into the boot from the battery, used the plug to plug the battery vent hole.

Did I do right? I just hope gas doesn’t build up pressure inside the battery and blow something up b/c it can’t escape. :grimacing:

(Andy) #2

Yes there should be a right angled plastic to connect between the battery and tube.

The plug is for transportation only, so you need to remove it. IMPORTANT!

Leaving it venting to the boot/trunk is not a long term solution due to rust, gasses etc

(Dick Wells,, 74 OTS UES1S25806BW, 99 XJR) #3

Agree with Andy. The battery must be vented to the outside of the car. Otherwise, vented gas will corrode and attack metal in the trunk!!! Even with the vent a periodic check, especially under the battery, is warranted. The gas is tin worm fertilizer .

Happy Motoring,


“Don’t let the Old Man in”


Ut oh, I’ll unplug it then until I can find a replacement for the angled piece you mention that apparently the PO lost. Hopefully local auto stores have something that will work as well … :crossed_fingers:

(Neil Bennett. Patron) #5

(Neil Bennett. Patron) #6

DAC77753 in unillistrated parts but NLA so a breakers is probably the best bet.

(Andy) #7

see the blue battery in this pic, with tube coming out


Well, technically, this is the set-up for the X-308s. But I see the vent tube there, too, although it’s not IDed. (btw, I never knew we were supposed to save the positive post cover off the battery to snap back over the post once the battery is installed. :flushed:


Ah, k … and what I need is that little white “elbow” fitting, it seems …

(Andy) #10

Search for

battery vent pipe

On eBay. About £5

(Neil Bennett. Patron) #11


I couldn’t find one on there specifically for face-lift XJSes. :slightly_frowning_face: However, one of our local chain auto parts stores has a generic one for sale, that is 8 mm. (about 1/4") in size (i.e. fits a vent hose that diameter). If I knew for sure that was the size of the Jag hose I’d go ahead and get it. Anyone know?

(Andy) #13

Well batteries are common across all manufactures, so i would like to think this is a universal part!

The only car specific part is the length of the tube.(The XJ8 one isn’t long BTW so can be cut) Anyway you have that part.

Sometimes these are supplied with batteries, so if you talk to your battery supplier you may get it free or discounted.

(Neil Bennett. Patron) #14

If the grommet is there the hole in the centre should determine the diameter of the tube!