Old Mercedes Filter: Venting a car battery?
August 22, 2013 11:04 AM   Subscribe

Old Mercedes Filter: I have an 82 Mercedes 300TD, I just bought a new battery and my tube to vent the battery isn't long enough. How necessary is venting the battery?

On my old battery there was a little hole in front for the venting tube, but this one only has a hole in the cover for the positive terminal, which I am going to take off once the battery is connected anyway. Thanks.
posted by Duffington to Travel & Transportation (8 answers total)
Is this a sealed battery or a vented battery?
posted by beagle at 11:40 AM on August 22, 2013

Most modern batteries are sealed and no longer require vent tubing. What model battery did you buy?
posted by cosmicbandito at 12:29 PM on August 22, 2013

A Duralast Gold Battery. Hopefully that link won't give you too much trouble, the main AutoZone page has a mind of it's own.
posted by Duffington at 12:43 PM on August 22, 2013

Caveat: I don't know anything about Mercedes. I do know a bit about batteries.

"Sealed" is a bit of a misnomer, used by marketing and shipping people. Many modern batteries are valve-regulated, meaning they try to keep gases in the cell for recombination, but can vent overpressure without damage. They're common in alarm systems, computer UPS units, and lots of places where they can "float charge".

However, such batteries are normally not used in cars. Most car batteries do have vents, as they charge pretty quickly just after a start, and that high charge rate can produce more gas than you'd want to manage with valves. The Duralast Gold product page specifically mentions vent caps.

Most cars simply put the battery in the engine bay, where gases can be vented without concern. It looks like the 300TD puts the battery under the passenger seat, which makes this problematic. I wouldn't worry too much about hydrogen gas (it dissipates very quickly), but it carries a whiff of sulfuric acid vapor with it, which likes to attack metal and corrode things. You'd really prefer that not to be confined.

Which, IMHO, makes the Duralast unsuitable for this car. It's not equipped for connection of a vent tube, which this car really requires. Return it. You might be able to get a vent-tube-capable battery for just a few bucks more. If not, call your favorite Mercedes mechanic and they'll point you in the right direction.
posted by Myself at 1:02 PM on August 22, 2013 [2 favorites]

I agree 100% with Myself, but would add that i'd go check out diesel mercedes messageboards and see what batteries are recommended, and what comments are made about whether this is important or not. There's a large community following for these cars(and one of them was my dream car for years, so i did a lot of research) and pretty much every available alley has been explored with this type of thing.

There's probably either a specifically recommended battery, or instructions to extend the tube. I really doubt the answer is "meh, ignore it". The 80s weren't that long ago, this isn't like converting a 6v VW bug to 12v or something where the old stuff is totally archaic horseless carriage material.

A lot of corners like this are ones you'd regret cutting later, especially on old, or even old-ish cars. And ESPECIALLY on fairly complex foreign cars. German cars can be over-engineered to a degree sometimes, but a lot of times(and especially on legendary models like these mercedes) that's part of what makes them so bulletproof.
posted by emptythought at 1:11 PM on August 22, 2013

My battery is in the engine bay, not under the seat. Sorry to threadsit, but this is the recommended battery from the generic auto parts store.
posted by Duffington at 2:23 PM on August 22, 2013

If it is in the engine bay I wouldn't worry about venting at all, most cars do not have any venting set up.
posted by deadwax at 3:19 PM on August 22, 2013 [1 favorite]

What deadwax said. If it's in the engine bay, you're fine, it does not need a vent tube.

A quick search had led me to some pages that suggested it was under the seat (including a diagram), and I based my advice on that bad information.
posted by Myself at 4:53 PM on August 22, 2013

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