Do I really need more vents for my batteries??

[DenverDMax]

Hello everyone, I have been searching for the past couple hours around various RV forums and cant find a definitive answer. I know if my batteries are in a (somewhat/totally) sealed box I need to vent the box, but if the batteries are open air under my front storage compartment do I need to add more vents?

The setup will be 2 6V golf cart batteries at about 235AH total capacity. I will be running three 12 volt 100 watt Renogy panels to them via a MPPT charge controller. My front storage compartment is a pass through style that also connects to the storage under my bed (queen size if that makes any difference). I have a hard time believing that with all the drafty areas around both front storage doors and around the underside of my bed that I will need to drill more holes in my storage doors for venting. The batteries will effectively be sitting in open air under the foot of the bed (not actually true open air but dang close).

Most of the posts I was reading were referring to sealed boxes or battery banks of much bigger sizes than mine. I have also read the equations for hydrogen off-gassing maximums and they just don't seem relevant to my small battery bank vs. cubed footage area. Any help is appreciated. I know that battery gas is corrosive and I know that acid is dangerous, if we could just focus on the venting aspect that would be very helpful.

Thank you,
JJ

 

[Trebor English]

A sealed compartment absolutely needs a pressure relief or a leak.  Otherwise you get pressure.  

A non pressurized compartment can still have a concentrated buildup of gasses.  If the compartment has doors with gaskets to keep out rain there won't be a flow of air to wash out the hydrogen.  If there is an identifiable source of air movement (computer fan) all is good, no buildup.  If the source of gas is at the bottom of a compartment convection will work if there is a big enough hole in the bottom to allow new air in as hydrogen rises.  No hole to allow air in, no air goes out.  

Spaces that don't have a forced air supply commonly build up strange fumes on boats.  Other than the lack of a river or lake, is a van any different?

 

[Trebor English]

It posted  twice.  Woops.

 

[Weight]

Charging wet cell lead acid batteries will have some odor. When heavily charging they will discharge some hydrogen gas along with oxygen. That is where the water goes, requiring them to be topped up on some regular schedule. Hydrogen is lighter than air and will try to rise and dilute. In a closed box the gases can build up and make an explosive mixture. Thus the need for ventilation. In a open compartment, you will have enough ventilation. If the odors disturb you, get a little muffin fan from a computer to dissipate the fume. Some folks are more sensitive than others. If really heavy over charging, there could be a mist of acid from the cells. That will cause corrosion on most any metal. My bank of EGC2 batteries are in a box with a vent fan blowing air into the cabin. I have no problem for 2 plus years with them.

 

[Spaceman Spiff]

 . . . I know if my batteries are in a (somewhat/totally) sealed box I need to vent the box, but if the batteries are open air under my front storage compartment do I need to add more vents? . . .

No.  Any compartment with a volume at lease 3 times the size of the batteries with a small amount of air circulation is OK.  Hydrogen is 0.000055% of air by volume.  It needs to rise to 4% to be flammable and 18% to be explosive in air at 14.7 p.s.i.a.  Problems arise when an enclosed battery box is not much bigger than the batteries, the batteries are being overcharged (outgassing a lot of hydrogen), and there is a spark source in the same box.  It is always best practice to separate any sparking sources from the compartment containing LA batteries.

As weight said some people are very sensitive to the smell of charging batteries.

 

[John61CT]

If you are that sensitive, then seal well from the living space, and

then you must vent to the outside, ideally passively and from the top.

Just like propane, but that's from the bottom, and much more critical to safety.

If like most people you aren't so sensitive, do not seal the box at all, in fact just strap them down, provide a bottom tray if flooded, and protect the posts from accidental shorts.

No danger issue then, your normal living space ventilation is enough.

Which could actually exit the space near your batts if you like to reduce any smell.

 

[bigskybob]

If I understand what you are asking,your batteries are in the open air.If so you don't need any venting.

 

[DenverDMax]

Thank you for the replies guys! My compartment is at least 20 times the size of the batteries that I will be using so I'm thinking I will be ok. Hopefully a quality charge controller wont be charging the batteries so hard that they will be off gassing for more than a couple hours a day. Thank you all for calming my nerves a bit!

Cheers

 

[QinReno]

There are multiple opinions on this, and some very strong ones. FWIW, see what these guys say about AGM outgassing. Enter " vent" in the search window.
https://batteryuniversity.com/learn/article/absorbent_glass_mat_agm

"yes, AGM and Gel batteries are safe for use in enclosed spaces.
only in serious overcharging situations do they vent some gas".

- re under the bed.
"Yes Michael, AGM will be perfectly safe for you.
both Gel and Agm vent a tiny bit when being charged hard, but it’s not enough to be considered even remotely dangerous or a risk".

 

[Weight]

Also see what I say about flooded cell battery.

 

[QinReno]

Also see what I say about flooded cell battery.

That sounds correct. If the batteries are not the sealed type, and require regular maintenance like topping off the electrolytes, then some sort of venting sounds like a good idea. Especially if OP smokes in bed, .

For my van, I think I'll stick with regular AGM, considering the small space and not wanting to cut holes in the walls or floor.