Battery Venting

[Ian_Rob]

Lead Acid Batteries are often supplied with a short length of tubing for gas venting purposes that will (quote), ‘allow any harmful gases to escape through the pipe once the end is placed outside your vehicle’. Placing the end outside the vehicle isn’t that practical, particularly on a boat. Do people actually bother with this or is it just assumed that it will dissipate naturally?

 

[dankilb]

My understanding is that - technically - they should be vented to the outside of the boat. This would typically involve a sealed box or compartment with a hose to a vent on the topsides (as one example). So the battery would vent into the box and the hose will then carry the gas safely out (it rises).

In reality, many installations don’t have this. It may be required for MCA coding etc.

I’m not qualified to comment on the safety implications, either way!

 

[pvb]

In a boat I think that any small amounts of gas will disappear on their own. Of course, with more people fitting AGM batteries, the problem is lessened. On my old Hallberg-Rassy, the battery boxes had tight lids and were connected to about 40mm diameter tubing leading to clamshell vents on the port and stbd coamings, so there was some ventilation.

 

[Caer Urfa]

All battery installations should be vented, Ideally if possible as PVB says to outside the boat, or many have batteries below seats in the saloon so should have a grill fitted as usually there is some fresh air flow from the saloon door/companion way access or windows, in engine bays they are usually vented via the engine bay ventilation ducts.

They also must be secured as in heavy weather it's surprising how easy it is for them to move about and risk serious damage

 

[pvb]

All battery installations should be vented,

Would you agree that this isn't really necessary for AGM/gel batteries?

 

[dankilb]

Might be worth checking this out (the explosion photo having been posted a few months ago by Paul in another thread…): That was interesting… Battery catastrophically died
[edit: apologies - originally linked to wrong concurrent battery thread above]

We currently have AGMs and when due for replacement will go LiFePo4. Otherwise, I would seal and vent our new box.

 

[LittleSister]

I have read on this very forum some time ago that the hydrogen given off by batteries when charging is not great in quantity, and easily escapes through relatively modest gaps in furniture, lockers etc. unless they've been deliberately made gas-tight, and IIRC dissipates relatively rapidly into the air. It is, of course, lighter than air and makes it way upwards and out of the boat. It is therefore very different from LPG. Note also that having given off hydrogen while charging, the battery will also need to absorb some again from the air when dischargarging.

In my view, while having vent grilles in lockers with batteries is a good thing it is not essential, venting them outside the boat is not necessary. I also wouldn't want to put a battery in an enclosed locker which also contains, e.g., an electric motor.


Other opinions are available.

 

[dankilb]

the hydrogen given off by batteries when charging is not great in quantity

I’ve read the same… but I assumed normal use wasn’t really the issue, but rather ‘failure mode’ (in which case if they boil or go bang, there lots of gas)?

 

[LittleSister]

I’ve read the same… but I assumed normal use wasn’t really the issue, but rather ‘failure mode’ (in which case if they boil or go bang, there lots of gas)?

The advantage of not venting overboard, or completely sealing the locker containing the batteries, is that you smell it when something is amiss well before before it goes bang!

I had a battery cell fail some years ago, and the smell was very obvious (the locker had no grilles, but gas easily escaped through the loose locker lid and tiny gaps in the furniture, etc.).

Even though I didn't attend to the battery problem for some time - in my ignorance I was initially thinking the smell was a problem with the adjacent toilet, and was asking on this forum for advice on that - all I ended up with was a slightly heat distorted battery.

Batteries going bang is very rare, as fr as I can tell. Even if a battery does goes bang, it's physically contained by the battery box (as shown in Paul's photo). Even a disintegrated battery doesn't contain that much hydrogen, so either the battery going bang will have used up all the gas, or what's left will, I expect, quickly dissipate upwards and into the atmosphere.

I have no problem at all with others going to great lengths to vent their batteries if they want to, but in my view it is unnecessary, and a long way down the endless list of safety 'would be nice to haves' on a boat.

 

[Graham376]

I have no problem at all with others going to great lengths to vent their batteries if they want to, but in my view it is unnecessary, and a long way down the endless list of safety 'would be nice to haves' on a boat.

Agree, some people worry too much in my opinion. Our four Trojans and engine start battery live in trays rather than boxes, in a vented-to-boat under bunk locker. Don't smoke in bed these days so not worried.

 

[Stemar]

The great thing about hydrogen is that it's a lot less dense than air, so dissipates quickly, unlike LPG which is mostly denser, so it accumulates in the bilges waiting for a spark to spoil your day.

H2S is also denser than air, but at least it won't blow you up. It might poison you, but I can't see anyone with a normal sense of smell staying around it long enough to suffer real harm.

 

[LittleSister]

H2S is also denser than air, but at least it won't blow you up. It might poison you, but I can't see anyone with a normal sense of smell staying around it long enough to suffer real harm.

I suppose getting poisoned by hydrogen sulphide is one way of finding out you've got Covid!