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Old 18-03-2019, 14:44   #1
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Do AGMs need battery boxes?

Hi all, I am the proud owner of three 4V Firefly VRLA AGMs 450Ah, which I plan to wire in series for our house bank. Due to their height, they will have to be mounted sideways to fit under the Q-Berth. Given that they are fully sealed and carbon mat AGMs, is it safe to go without the kind of battery boxes that you see with FLAs? Most are cumbersome and designed to have the connections on top i.e. don't lay on their side well. Can we forget the boxes and just strap them down well?
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Old 18-03-2019, 15:09   #2
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Re: Do AGMs need battery boxes?

They're sealed, and have a non liquid electrolyte, so no spill control technically required. As long as they're strapped down so they can't move or bang into stuff and the terminals protected from shorting they'll be fine. I use pieces of wood screwed down beside the batteries and underlying rubber sheeting to prevent them from wanting to slide around in rough weather.


Just a heads up though, I have an AGM that has a leak at one of the terminals so do keep in mind that they can "leak", just not in a way that spills out liquid.
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Old 19-03-2019, 14:42   #3
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Re: Do AGMs need battery boxes?

Any lead batt can leak / explode.
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Old 20-03-2019, 07:16   #4
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Re: Do AGMs need battery boxes?

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Originally Posted by john61ct View Post
Any lead batt can leak / explode.
Not a very helpful posting!

Any boat can leak or explode!

To answer the OPs question AGM batteries that are designed for marine use will be tough enough to fall repeatedly off three metre waves. Not all AGMs are created equal so don't buy cheap AGMs that are designed for solar or standby Telecom use.
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.....Just a heads up though, I have an AGM that has a leak at one of the terminals so do keep in mind that they can "leak", just not in a way that spills out liquid.
So what kind of 'leak' did you have with what brand of AGM? They are usually pressurised to about 5 PSI so any 'leak' would be permanently venting H2 and O2 - put water on the 'leak' and you would see bubbles.

My AGMs have no battery boxes and my Red Flash engine start also has been lying on its side for 14 years with no signs of any corrosion on the support wood or the terminals. They all look perfectly clean, but have never been touched - unlike FLA batteries that will always vent and corrode wires and terminals.
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Old 20-03-2019, 07:44   #5
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Re: Do AGMs need battery boxes?

Sorry I thought my reco was clear.

Of course if you are lucky enough to never have a catastrophic accident,

which being meticulous about proactively replacing your bank long before it fails certainly helps the odds,

then you may never regret failing to keep your your AGMs in a proper box or at least a tray to catch electrolyte.

Personally I don't recommend it.
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Old 20-03-2019, 09:34   #6
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Do AGMs need battery boxes?

AGMís canít leak, or leak significantly and therefore donít need boxes.
The are ďnon spillableĒ and that is why they can be shipped as not being hazardous cargo, a wet battery canít and therefore is usually shipped dry.
As far as explosion, never heard of it in an AGM but anything is possible, however I doubt a thin plastic box is going to do anything in an explosion.
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Old 20-03-2019, 10:26   #7
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Re: Do AGMs need battery boxes?

AGMs electrolyte is a gel on a glass mat, hence the name. They might be able to explode, but they will not leak. If a battery explodes, I seriously doubt a thin plastic box is going to contain the debris.
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Old 20-03-2019, 13:08   #8
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Re: Do AGMs need battery boxes?

I have seen plenty of cracked and split AGM lose enough electrolyte to damage the surface below.

Even just from overcharge venting, the acid can condense and drip.

Certainly just a proper tray would be better than nothing, true "explosions" are pretty rare.

But if you want to go completely bareback, your rig your choice.
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Old 20-03-2019, 14:55   #9
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Re: Do AGMs need battery boxes?

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I have seen plenty of cracked and split AGM lose enough electrolyte to damage the surface below....
Plenty .... how many and what makes. Are you a dealer or a marine engineer who doesn't like AGMs? You still have no details in your profile for any readers here to believe a word you say.

AGMs cannot leak electrolyte as the Glass Matt is only 95% saturated. I have seen people who have 'filled up' their AGMs with electrolyte which may well cause some kind of expansion of the shell causing a leak.
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Old 20-03-2019, 15:17   #10
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Re: Do AGMs need battery boxes?

I have nothing against AGM, when the need for what they offer exceeds the higher cost over time

"cannot" LOL

Feel free to believe or not, no difference to me
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Old 20-03-2019, 15:21   #11
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Re: Do AGMs need battery boxes?

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Originally Posted by sailinglegend View Post
Not a very helpful posting!

...
So what kind of 'leak' did you have with what brand of AGM? They are usually pressurised to about 5 PSI so any 'leak' would be permanently venting H2 and O2 - put water on the 'leak' and you would see bubbles.
..

The kind of "leak" where stuff comes out the guts of the battery. Not as a liquid, but as a damp salt like substance very similar to that which can appear on FLA terminals at times. This is a cheapo chinese battery used as secondary bank that and the leak is between a terminal and the case. It is 5yo though, and still works "adequately" although not as good as the 6yo primary bank.
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Old 20-03-2019, 15:27   #12
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Re: Do AGMs need battery boxes?

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AGMs electrolyte is a gel on a glass mat, hence the name. They might be able to explode, but they will not leak. If a battery explodes, I seriously doubt a thin plastic box is going to contain the debris.

I've seen a couple of nearly new AGM's wired in parallel that were destroyed by unregulated charging. The cases where covered in osmosis like blisters cause by, I suspect, the temperature of the battery and pockets of gas. Not sure if they eventually vented or not, but they were absolutely fried. I couldn't see any splits in the casings or evidence of chemicals, so the cases held together ok.
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Old 20-03-2019, 19:02   #13
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Do AGMs need battery boxes?

Iím sure they vented, if you desire to hear one vent, short it out, within a few seconds it will hiss at you like a snake.
In aircraft I think they vent pretty often, take one to 20,000 ft and the pressure drop will have it vent Iím pretty sure.
Then descend and the battery will have a sucked in appearance.
In classes Concorde gives, they even have a slide about the bulging and sucked in sides being normal.
Itís part of a ďsealedĒ battery.
Concorde is the parent company that manufacturers the Lifeline AGM, Iíve been told they are essentially identical.Click image for larger version

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Old 20-03-2019, 19:56   #14
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Re: Do AGMs need battery boxes?

ABYC requires (and makes no exceptions for AGM's) ............

10.7.1 Battery mounting materials and surfaces shall withstand electrolytic attack.

10.7.2 Provision shall be made to contain incidental leakage and spilled electrolyte


There was almost no electrolyte left in this AGM and no tray to catch it..
The wing nut is not kosher either
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Old 20-03-2019, 20:00   #15
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Re: Do AGMs need battery boxes?

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Iím sure they vented, if you desire to hear one vent, short it out, within a few seconds it will hiss at you like a snake.
In aircraft I think they vent pretty often, take one to 20,000 ft and the pressure drop will have it vent Iím pretty sure.
Then descend and the battery will have a sucked in appearance.
In classes Concorde gives, they even have a slide about the bulging and sucked in sides being normal.
Does that apply to sea level ?
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