Lead acid battery venting

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Lead acid battery venting

Postby rustytoolss » Tue Sep 05, 2017 9:52 am

I am going to used a lead acid 12V car battery for my 12V system. I have a steel enclosed battery box . I also will have it vented from the top of the lid/ to the outside of the camper. The battery will be mounted in a cabinet/ in the cabin of the camper.
Do I need to provide a lower air intake/vent , to provide good airflow in the bottom of the box ? And run the intake tube through the floor ? :thinking:
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Re: Lead acid battery venting

Postby troubleScottie » Tue Sep 05, 2017 10:17 am

The concern is vented hydrogen gas -- explosive and much lighter than air.

You should be fine with a single vent higher than the battery and no cavities to catch hydrogen. The actual flow should be very small.

Obviously the other issue is sulfuric acid leaks. That should be handled by the container.
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Re: Lead acid battery venting

Postby John61CT » Tue Sep 05, 2017 1:04 pm

no active venting needed, just not letting it build up
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Re: Lead acid battery venting

Postby SSTear » Tue Sep 05, 2017 1:07 pm

Just posting this for those who have limited or no venting to their battery compartments. I use this sealed battery that does not emit fumes and is sealed. I tested this non stop for a week running my fantastic fan on med speed and it still had 30% charge after that.

https://www.windynation.com/Batteries
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Re: Lead acid battery venting

Postby rustytoolss » Wed Sep 06, 2017 8:39 am

Just did not know if I would need the lower vent , to increase the venting process. But , good to know that I may not have to drill an extra hole in my floor :) .
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Re: Lead acid battery venting

Postby MtnDon » Wed Sep 06, 2017 8:53 am

The acid fumes that occur when being charged will eventually cause corrosion with the steel box. Epoxy paint might slow that down.
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Re: Lead acid battery venting

Postby rustytoolss » Wed Sep 06, 2017 9:56 am

Thanks for that information, I may get a different box.
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Re: Lead acid battery venting

Postby mary and bob » Wed Sep 06, 2017 3:27 pm

Adventure RV sells a vented battery box for about $30. Comes with a hose and wall vent. With a plastic box you can just drill a couple holes in the side, put bolts through for your connections. That's how our Uhaul camper was set up from the factory. However they had the vent through the wall mounted too low (hose should run uphill from the box) so I found a boat gas tank vent on eBay and installed it through the wall higher up.
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Re: Lead acid battery venting

Postby working on it » Wed Sep 06, 2017 4:07 pm

  • I've found that venting is really only needed when charging, at higher charging rates; trickle charging doesn't produce much hydrogen, as I have tested that effect many times, personally. I formerly used my HHR Panel as a icy-weather sleepover base (when I couldn't commute 120 miles on ice, before I retired), and would sleep with my head directly over where the battery was, under the rear floor. The vent tube was broken after about a year, and I didn't replace it, so I slept in that un-vented vehicle at least 20 times, and never once detected any gas. Even after I would drive it for hours (with the alternator charging), and open the rear hatch, I never smelled any hydrogen (cars aren't built to be airtight, unlike my TTT squareback, which is, almost).
  • I also had three VW bugs, back in the day, and only once smelled hydrogen, when the generator was overcharging, due to a faulty voltage regulator (the batteries of old VW bugs was under the rear seat). Unless your battery box sits near a spark source, or open flame, I wouldn't worry too much about it; just have the vented box in a safe location. As for possible battery acid spills and/or corrosion, I've used acid absorbing mats under some of my batteries, when I expected rough conditions to possibly spill some acid, or when I intentionally charged my batteries at an extremely high rate (between rounds, when drag-racing my Chevelle).
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    acid absorbing mat.PNG (160.11 KiB) Viewed 301 times
    if you use a metal battery box or tray, this is needed
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Re: Lead acid battery venting

Postby martymcfly » Wed Sep 06, 2017 7:31 pm

If you are getting fumes, you are overcharging your battery. I am not even sure that you need to vent anywhere. The most produced model of car ever (vw bug) had a battery mounted under the back seat, with an ashtray about 2 feet away. Not vented. They made them that way for 50 years and never changed, so there must not have been any problems.
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Re: Lead acid battery venting

Postby beezerboy » Fri Sep 08, 2017 9:36 pm

get an AGM type - absorbed gas mat. these are sealed & there is no leakage. there is none of the traditional servicing hassels we had with flooded cell batteries either. in addition, most can be installed in any position other than up side down. there is no reason to put a wet cell battery in anything anymore. as mentioned, they can gas if over charged. gas will escape through a vent valve in the case that is there only to keep the case from blowing up. in the ideal service life of this type battery, no gas is ever lost, all the gasses are re-absorbed in the mat (recumbent gas technology). if you worry, line the box with a piece of felt & soak it with baking soda once a year.
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Re: Lead acid battery venting

Postby MtnDon » Fri Sep 08, 2017 10:31 pm

martymcfly wrote:If you are getting fumes, you are overcharging your battery. I am not even sure that you need to vent anywhere. The most produced model of car ever (vw bug) had a battery mounted under the back seat, with an ashtray about 2 feet away. Not vented. They made them that way for 50 years and never changed, so there must not have been any problems.


There are several sources for floor pan repair kits for the old beetles, made specifically because floor corrosion under the battery is commonplace and is due to the hydrogen being released as well as the mist that is carried along with the gasses.

Any time a battery is charged H and O2 are both given off by that normal chemical reaction. That can and does cause very small amounts of liquid to be expelled from the battery cells as a fine mist. It happens with any flooded battery. Every flooded battery I have installed in an off grid system eventually ends up with the tops of the batteries slightly moist with acid. Those are systems with high quality charge controllers... no overcharging going on. (There are special caps available for off grid use that have catalyst pellets in them and cause the H and O2 to recombine and drop back into the cells. Batteries with those caps usually have drier tops and less corrosion.)

I leave a copper penny on the battery top beside each terminal. The penny is sacrificial and corrodes before the terminal connections. But it does not stop the charge gassing or misting.

That is an advantage of an AGM battery. No gassing under normal use. But I like to check cells with a hydrometer and keep a log of the readings over the years. That helps see what the battery health is. But I baby my batteries more than most folks. I have used AGM batteries in my off road vehicles for decades though.
Last edited by MtnDon on Sat Sep 09, 2017 12:19 pm, edited 2 times in total.
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Re: Lead acid battery venting

Postby John61CT » Sat Sep 09, 2017 11:05 am

So much misinformation.

FLA batts offgas every time you properly charge them to 100%.

Same with AGM, just a lot less.

If you seal batts in a box you should vent.

If you don't mind the smell, then little danger, most of the time, to allow to dissipate in the living space.

But batts can explode if you don't keep an eye out, should be replaced when capacity drops by 25-30% at the most.

Most people just ignore SoH, keep the batt way too long.

In which case best to seal and vent to outside.
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Re: Lead acid battery venting

Postby rustytoolss » Sat Sep 09, 2017 4:19 pm

All of the 1964-1970 Dodge vans and A model pickups had the battery directly behind the drivers seat, in a steel box. It vented out the bottom. I've never smelled anything in my 64 A100 pickup. Or my fathers 1970 Dodge widow van, purchased new in 1970.
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Re: Lead acid battery venting

Postby GPW » Sun Sep 10, 2017 5:29 am

We always kept the batteries in a plain unfinished wooden box ..

Has anybody tried the battery rejuvenation trick as seen on U-You Tube ?
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