AGM Battery Venting

[3bcamper]

I inquired about additional batteries, and my local Airstream dealer said that AGM batteries don't need to be vented to the exterior, as opposed to liquid/sulphuric acid type batteries.

The service manager said additional batteries could be installed directly in the occupied space.

Thoughts, opinions, experience, objective facts to the contrary?

[Protagonist]

Originally Posted by 3bcamper

I inquired about additional batteries, and my local Airstream dealer said that AGM batteries don't need to be vented to the exterior, as opposed to liquid/sulphuric acid type batteries.

The service manager said additional batteries could be installed directly in the occupied space.

Thoughts, opinions, experience, objective facts to the contrary?

The original Interstates had a single AGM house battery located under the front passenger seat, not vented to the outside at all.

AGM batteries do out-gas when charging, but the amount of hydrogen released is so small, and the volume of the van's interior is so large, that it would be all but impossible for the hydrogen concentration to reach a level that is explosive or unsafe to breathe.

[RandyNH]

But still not in normal circumstances: (outgassing)

VRLA batteries

During rapid recharging, the electrolyte may boil and pressurize the case, or gas build-up may be too rapid for recombination. These effects necessitate the “valve regulation”. This is normally in the form of a one-way pop-off valve that only opens in the case of pressure build-up. Even if the valve pops, the immobilizing agent prevents rapid, or any, acid leakage. Most designs are so stable and contain so little electrolyte that they won’t leak acid even if they are cut open.

[J. Morgan]

Originally Posted by RandyNH

But still not in normal circumstances: (outgassing)

VRLA batteries

During rapid recharging, the electrolyte may boil and pressurize the case, or gas build-up may be too rapid for recombination. These effects necessitate the “valve regulation”. This is normally in the form of a one-way pop-off valve that only opens in the case of pressure build-up. Even if the valve pops, the immobilizing agent prevents rapid, or any, acid leakage. Most designs are so stable and contain so little electrolyte that they won’t leak acid even if they are cut open.

Reading that, makes me want to seal them out of my house anyway.

My next upgrade will move the batteries inside, now I know I will be building a battery box sealed from the trailer body for sure.

I know they stink pretty bad if you pop a vent because of over a single overcharging episode.

That would suck.

[Titus]

Interesting that the older AI has a single in-vented battery under the front seat while my AI lounge EXT has two batteries in the back in a sealed box that is vented to the outside. Hard to imagine that Airstream would have spent the money on a sealed box and cut a hole in the van body without a need to do so.

BTW, I also use the vent hole in the battery box to run the negative battery cable from my battery monitor shunt to the negative battery terminal. This way I am able to capture all current going to/from the batteries. In original design the negative side of the Sprinter charging was missed because it got to the batteries by way of the grounded battery box.

[3bcamper]

Originally Posted by Titus

Interesting that the older AI has a single in-vented battery under the front seat while my AI lounge EXT has two batteries in the back in a sealed box that is vented to the outside. Hard to imagine that Airstream would have spent the money on a sealed box and cut a hole in the van body without a need to do so.

BTW, I also use the vent hole in the battery box to run the negative battery cable from my battery monitor shunt to the negative battery terminal. This way I am able to capture all current going to/from the batteries. In original design the negative side of the Sprinter charging was missed because it got to the batteries by way of the grounded battery box.

I'm guessing that Airstream had safety in mind when they installed the vented box. They would have no control over what type of battery owners may install later when replacing original batteries.

[Titus]

good point about switching battery types.

[J. Morgan]

If there were to ever be a battery fire, a metal enclosure might give an occupant another 2 to 3 minutes to evacuate.

Whenever I think about shirking the idea of a metal enclosure, that point kind of sticks in my mind.

The odds are slim of there being a battery fire if everything is done right and kept proper, but that doesn’t always happen.

[rmkrum]

At least on my AS there is no safety fuse installed right on the battery positive post. There will be one there shortly.

My box is plastic, but mounted external to the interior.

[J. Morgan]

Originally Posted by rmkrum

At least on my AS there is no safety fuse installed right on the battery positive post. There will be one there shortly.

My box is plastic, but mounted external to the interior.

My batteries are external not boxed and not fused real close to the batteries right now, (but with a lot of effort expended to insure no short circuits), but since I am moving them inside I am going to install circuit breakers at both the positive and negative posts and making a box to enclose them.

I was thinking about getting lazy, moving to AGM’s, and foregoing the box, but It will only take a little while to build a box, and it will make me sleep better.

[uncle_bob]

Hi

The risk with an AGM is a shorted cell. In that (rare) case, you feed way more into the remaining good cells than they are happy with. If you have a pair of batteries in parallel, there is a lot of current available when a cell shorts. Even in a single battery setup, the converter or alternator is going to over voltage / over current the battery. In both cases, you get way more gas than you ever would in a normal charge situation.

Yes, it's a cascade failure. Shorted AGM's are rare. Explosive gas mixtures aren't real easy to come up with. How much the combined risk worries you .... that's up to you.

Bob

[PKI]

Hydrogen is a very small particle. It will pass through any material that is somewhat porous. Example is a normal building roof. A sealed steel or aluminum box will trap the gas and should be vented. The flat lid on an AS battery box likely does not trap Hydrogen as H2 is lighter than air and would escape out the sides of the lid. Pat

[Protagonist]

Originally Posted by PKI

Hydrogen is a very small particle. It will pass through any material that is somewhat porous. Example is a normal building roof. A sealed steel or aluminum box will trap the gas and should be vented. The flat lid on an AS battery box likely does not trap Hydrogen as H2 is lighter than air and would escape out the sides of the lid. Pat

Hydrogen rises. It does not rise, then fall, then rise again to maneuver around the lip of a box lid. So it is possible for a battery box to have an accidental hydrogen trap if the vent is not at the very highest point of the lid.

[J. Morgan]

Originally Posted by Protagonist

Hydrogen rises. It does not rise, then fall, then rise again to maneuver around the lip of a box lid. So it is possible for a battery box to have an accidental hydrogen trap if the vent is not at the very highest point of the lid.

To me battery outgassing just stinks, the chances of the mixture being right for explosion and fire are slim. I like a metal box in case of fire. It will buy some time, and maybe even smother a fire before it gets big.

[PKI]

Originally Posted by Protagonist

Hydrogen rises. It does not rise, then fall, then rise again to maneuver around the lip of a box lid. So it is possible for a battery box to have an accidental hydrogen trap if the vent is not at the very highest point of the lid.

Pro - yes, but I believe the lid on the existing trailer boxes is flat. A lid configured as an inverted tray would function as the trap you describe. Pat

[Protagonist]

Originally Posted by J. Morgan

To me battery outgassing just stinks, the chances of the mixture being right for explosion and fire are slim. I like a metal box in case of fire. It will buy some time, and maybe even smother a fire before it gets big.

Not arguing with you. Just saying the vent in the box needs to be in the right place, that's all.

The volume of air in a battery box is small because the batteries themselves occupy so much of the box's volume, so it doesn't take very much hydrogen to reach the lower flammability limit of 4% hydrogen by volume (or even the lower explosive limit of 18.3% hydrogen by volume) in the remaining air space inside the battery box.

So by all means use a metal battery box. But if the vent isn't in the lid itself, then just make sure that you either place your vent in the box's lid, or make sure the lid has no lip around the edge that could form a hydrogen trap.

[J. Morgan]

Originally Posted by Protagonist

Not arguing with you. Just saying the vent in the box needs to be in the right place, that's all.

The volume of air in a battery box is small because the batteries themselves occupy so much of the box's volume, so it doesn't take very much hydrogen to reach the lower flammability limit of 4% hydrogen by volume (or even the lower explosive limit of 18.3% hydrogen by volume) in the remaining air space inside the battery box.

So by all means use a metal battery box. But if the vent isn't in the lid itself, then just make sure that you either place your vent in the box's lid, or make sure the lid has no lip around the edge that could form a hydrogen trap.

Point taken Pro. Thank you.

[Protagonist]

Originally Posted by PKI

Pro - yes, but I believe the lid on the existing trailer boxes is flat. A lid configured as an inverted tray would function as the trap you describe. Pat

The OP posted in the "Sprinter and B-Vans" forum, and that's what my replies were meant to address. If we're now talking about trailers with an external battery box, that's a different subject than an interior battery box in an Interstate.

[PKI]

Originally Posted by Protagonist

The OP posted in the "Sprinter and B-Vans" forum, and that's what my replies were meant to address. -- snip --.

Understand - is the same venting appropriate for that rotten smelling H2S? Pat

[J. Morgan]

Originally Posted by PKI

Understand - is the same venting appropriate for that rotten smelling H2S? Pat

I think that would vent heavier than air, so a person would want a vent on the bottom that would double as a drain in addition to the top venting.