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2000 Passat B5 wagon, 4-Motion, 2.8l ATQ
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Discussion Starter · #1 · (Edited)
’00 Passat 4Mo wagon, 2.8l ATQ

About 6 years ago, the VW dealer replaced the battery with an Interstate product, I believe. Then, three years ago, that battery died, and was replaced by an EverStart MAXX H6, which cost about half as much, not at the dealer. I believe they are both made by Johnson Controls. The EverStart also lasted about 3 years, but fortunately, I got a free warranty replacement, which I just installed.

Neither the dealer nor the last installer hooked up a vent tube to one of the open battery vents. The new battery came with an elbow for such a purpose. I assume there was a vent tube attached at one time, but I am not the original owner and never saw one. On YouTube videos, most [professional?] installers I watched did not bother with the vent.

On the prior battery, the terminals and cable clamps have remained clean and free of corrosion.

I attached a photo of an open port in the wall which I’m guessing could be for the battery vent.

Any opinions on whether to re-install a vent tube to the battery? If so, what inner and outer diameter tube should I be looking for? And is the open port circled in the photo the one for venting the battery?

Thanks in advance for your feedback.

battery-vent1.jpg
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Update:
As noted by KSEADUB, clearly, the port I circled leads nowhere.
 

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Modern batteries don't outgas during charging like the old ones, which is also why 'Gel-Cell' lead-acid batteries can be completely sealed. I think that you can skip the vent hose.
 

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Not totally true. Even modern ‘maintenance free’ batteries offgas. Only AGM batteries (which still give off some gas but not nearly the amount standard lead acid batteries do) don’t need to be vented. If the battery you bought came with vent tubes, you should use them.

There should be a grommeted hole in/near the floor of the battery tray that you can use to run a vent line. The picture seems to show some sort of grommet that runs through the false firewall by the brake master cylinder. Thats not meant for the vent tube.


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Depends on where you live. If you live in AL, AZ or any place with "5 months of summer", you can install the vent tube; but I never have (5 batteries in a '99 AEB Passat). Average length summers, and you'll be fine skipping it as ylwagon said.

Most of what evaporates from the sulfuric acid water "electrolyte" mixture is good old distilled water, which is what you should add if and only if the level in each cell has dropped so low that you can no longer view a meniscus at the liquid surface. I never add more than ~5ml per cell when topping up...roughly once every 24 months depending on whether the car is garaged or sits in direct sunlight daily for 14 hrs in July/August.

:beer:
 

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Actually, it's not water vapor, it's hydrogen gas. Now, I'm pretty knowledable about batteries, and I'd evaluate the risk of venting tiny amounts of flammable gas into the plenum as very small... but apparently VW engineers disagree with me. I buy (surprisingly inexpensive) original VW batteries, and they still have the vent. I hook it up. My 2000 was missing the hose and elbow when I bought it used, and the dealership sold me both for about $5.
 

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2000 Passat B5 wagon, 4-Motion, 2.8l ATQ
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Discussion Starter · #6 ·
The devil's advocate would ask: What is the probability of damage from the vent [tube] beneath the car getting clogged vs. the probability of plenum vented gases igniting if not using a vent tube? I certainly don't know. The MAXX batteries appear to be mostly sealed (no non-destructive means to add water).

I checked a totally different beast, my dad's '17 Subaru, and they decided not to use exterior venting - the Johnson Controls battery therin doesn't have vent ports, but does have caps for adding water and/or venting.
 
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