Do I need a battery box ?

[DaveS]

Our previous posts crossed. Most of the considerable number of experiences quoted in your second involve starting a car (or, occasionally, a boat) engine a few minutes after it's been previously going and presumably (over)charging the battery, causing gassing. This scenario is understandable (if rather disconcerting for the participants!)

I still fail to understand where the hydrogen is supposed to come from in the scenario of a battery being unused or discharged for hours / days / weeks.

 

[DaveS]

Another crossed post! I have no issue with most of what you say, but I would ask again in what circumstances, other than being vigorously charged, would you consider that a battery would emit hydrogen?

 

[boatmike]

Batteries give off some gas all the time when in use, but if the charge discharge rate is low so will the emission of hydrogen be. A good measure of how much your own gives off is how often you need to top up your water. If frequently=a lot. If seldom=a little.
To answer your other point a battery with very low water level will get hot. Even if deeply discharged ( to all intents and purposes flat) it will contain hydrogen and oxygen which in so called sealed batteries can't escape. So a flat battery can explode very easily. Thats why I said they are seldom "dead" or "inert" just deeply discharged.
"Sealed" batteries are therefore more prone to internal explosions through components shorting internally where vented batteries are more likely to give off more hydrogen and cause an external problem if not installed properly but are less prone to internal explosions

 

[Stoaty]

Batteries can explode. Most times it is caused by people removing charger leads from a battery that has just been charging before disconnecting the power and so causing a spark. There is little gassing of batteries being charged at less that 13.8 volts, so little risk below this voltage. Hydrogen atoms are very small and light. They will rise quickly and find ways out of enclosures easily. I was once told they can pass up the thread of a screw. The only real risk is from a spark or naked flame close to the battery when it's near the end of it's charging cycle. Considering the number of cars on our roads, if battery hydrogen was dangerous, the streets would be littered with blown up people and bonnet less cars. I don't use a battery box. My batteries are in two lockers under the seats in the cabin.

 

[DaveS]

Not having a go, but I'm really struggling to understand this. [ QUOTE ]
Batteries give off some gas all the time when in use

[/ QUOTE ] Do you mean this literally, or do you really mean "when they are being charged"?

[ QUOTE ]
to answer your other point a battery with very low water level will get hot. Even if deeply discharged ( to all intents and purposes flat) it will contain hydrogen and oxygen which in so called sealed batteries can't escape. So a flat battery can explode very easily. Thats why I said they are seldom "dead" or "inert" just deeply discharged.

[/ QUOTE ] So, if I understand correctly, you are saying that deeply discharged batteries which also have a low water level can pose a hazard. I do not really dispute this, but was querying the oft-quoted advice re. jump starting cars where low battery water level, because of the typical car battery usage cycle, is relatively rare.

 

[boatmike]

I agree hydrogen gas will certainly escape easily if there is a route for it to do so. Enclosed lockers under seats often don't allow it to escape easily enough though and thats certainly not ideal. You mention only one source of sparking. Another is as I said before, starter motor brushgear. More than one boat battery has exploded on starting the engine when the batteries were sited right under the starter. Actually the situation with cars is very different. The current demands and charging rates are very much lower and of course the engine is running all the time you are drawing current so the current draw and hydrogen emissions will be much lower. Also the battery is by no means in a sealed compartment.

Its very difficult to analyse precisely why an explosion takes place but I have one clear experience of a build up of gas in a locker adjacent to the stove under a quarter berth bunk. Sufficient gas escaped from the battery (which was on charge from a shore lead at the time) to be ignited by the stove being lit which blew the top off the bunk and split the GRP vertical sides of the locker open. Luckily the only casualty was that the owner is now permanently deaf in one ear and has a few ugly scars on his legs.
I am not quoting all these things to be a doom and gloom merchant. It's just that most people think batteries are harmless things that can be sited anywhere and never maintained until they fail. Battery explosions are not very common but not as rare as most people think either so we should be aware.

 

[Stoaty]

[ QUOTE ]
A good measure of how much your own gives off is how often you need to top up your water. If frequently=a lot. If seldom=a little.

[/ QUOTE ]

This is a little misleading. Some fluid is lost as hydrogen is given off during gassing. There are other reasons why fluid is lost in flooded lead acid batteries. During charging the battery temperature will increase and fluid is lost by evaporation. If the electrolyte temperature reaches 2.5°c above the ambient air temperature fluid loss by evaporation will begin and become higher if the temperature difference gets bigger.

Keeping your batteries in a hot engine room does them no favours at all. You will also find that in the summer fluid loss is greater than the winter simply due to higher air temperature.

To be pedantic, in the trade, batteries that fail (blow up) through internal failure, usually caused by bent plates shorting out, are referred to as melt downs. This is a more accurate description of what goes on inside although in extreme cases it can be quite violent. Most batteries that fail suddenly without warning and appear to be sound have in fact suffered a slow melt down and self discharged.

 

[boatmike]

Sorry. While you are correct that temperature has an effect, the main cause of water loss is "cracking" the H2O down in to its components of hydrogen and oxygen. Water does not evaporate from a modern sealed battery to any great extent and batteries on cars which are not usually heavily discharged or "deep cycled" seldom need water levels checking over long periods even in hot climates. This has given rise to the term "maintenance free" (which is a term that should only be believed if on a motor vehicle in regular use). It is impossible to stop hydrogen escaping however even from a so called "sealed" battery. As someone else said the atoms of hydrogen are very small and batteries are designed to allow it to escape. If you didn't the casing would split with the pressure. Water vapour however has more mass and cannot escape the same way. On an older type battery which is more positively vented, some evaporation takes place, but even then if the battery is not used over a long period the water level seldom varies appreciably even in high temperature.

 

[Daesal]

Sorry to revive such an old thread but just in case it is useful and helps anyone safety:
A word of caution.
Batteries do explode...not often but for various reasons sometimes they do.
Years ago on a very very hot day 5 of us were sitting around in the cabin
Under the seat was the battery - a non maintenance free lead acid battery 80ah
The conversation got round to if this was safe
The man sitting on the bench said that there were lots of horror stories,but really had anyone really heard of anything bad happening.
A couple of beers later we all agreed through limited knowledge and absolutely no research except heresay that it's safe and people love a disaster story so batteries dont really explode,especially under a seat , in a cabin , where it was a bit stuffy but cooler than the outside.
With this decided we went for a walk .
We had just left the cabin and were not 3 min out the door when there was an almighty bang.
While minor damage was done,the seat was pulled off the hinges. The cushions thrown across the cabin . With the size of the bang I'm glad no one was inside at the time.
I'm also glad the battery wasn't under the kids bed during siesta time.
Theres lots of reasons why batteries "shouldn't explode" but always best to go on the side of caution when choosing where to locate them.
However there is a happy ending to that story. During the conversation the man who installed the battery said:"If that battery explodes I will buy ye all a cold beer".
Minimal damage and cold beer later. Just glad no one was inside at the time.

 

[Beneteau381]

I plan to fit 2 additional 110Ah batteries at easter but Im just wondering if they need to be in a plastic battery box. They will be sealed, maintenance free type so no chance of splilling acid ? They will be under a sturdy wooden seat with good restraints to stop them moving, so physically secure, and Ill put appropriate electrical insulation around to prevent shorting the terminals.
So - do I really need a plastic battery box ?
What does the panel think - false economy? - If so why ?
Thanks
Steve

I fitted a sturdy piece of ply for the base with battens screwed to that to hold them in place.Straps off things screwd to the ply to secure them. Ten years in place and not an issue. Top tip, the so called sealed ones usually have a breather at each end with fittings to attach a breather pipe. I got a plastic pill bottle, put some bicarb in and led the little hoses to it. My thoughts being that it would neutralize the acudic breathing gases.

 

[[163233]]

Sealed batts will require a vent to release gas, there's a valve on it which is why they can claim sealed.

Having just replaced my batts which were killed by covid, and mocked for the feeble size of the bank (140ah). It occurred to me that I could get substantially larger batteries in the compartment if I ditched the plastic boxes. However, the boat is coded so must adhere to mgn280, and having just checked, that doesn't appear to require plastic trays.

I've replaced them with equivalents now so I'll probably live with it.

 

[Rappey]

I was offroading with a friend when his machines just died. Seemed a battery problem.
We lifted the seat to find the plastic sides of the battery had parted, fallen off , spilling all the acid over his machine !
Probably very rare but there are enough cheap battery boxes on ebay to house batterys without breaking the bank.