Building A Battery Box For AGMs

[Delancey]

I'm building a battery box for my AGMs. Part of the reason I spent the $$$ for AGMs was to not have to worry about spilling acid.

Seems like I could provide better ventilation for the batteries if cut holes in the bottom of my box and didn't worry about trying to collect any acid that I theoretically shouldn't have to worry about spilling from my batteries.

Any thoughts?

[Stu Jackson]

Dumb idea. Vent the "compartment" that holds the boxes and you're done. It's almost an "urban myth" about battery fumes anyway, but venting the area is always helpful.

[Maine Sail]

Originally Posted by Delancey

I'm building a battery box for my AGMs. Part of the reason I spent the $$$ for AGMs was to not have to worry about spilling acid.

Seems like I could provide better ventilation for the batteries if cut holes in the bottom of my box and didn't worry about trying to collect any acid that I theoretically shouldn't have to worry about spilling from my batteries.

Any thoughts?

There is no requirement to build an acid containment box for AGM batteries. They do need ventilation, and proper hold downs, but do not need a box.

[a64pilot]

If it were me, I'd size this box so that it could hold GC batteries, just in case you later decide to go that route, Mine can't or I would have.
I may be corrected but I'd like to have an inch or so around each battery if possible and I too doubt ventilation will be an issue unless you try to seal the lid, it doesn't take much to ventilate the box.
Probably silly, but I have a piece of cheap corrugated bilge pump hose routing Air Conditioning air into my box, idea being is if it's hot and I'm charging hard, likely I'm on shorepower and the AC is on, idea being to try to keep them as cool as possible, but also I guess it's forced air ventilation.

But, I think most AGM batteries are Recombinent Gas? Meaning through some form of magic I don't understand they recombine the gasses to make water is why you never need to add water.
Also I think most are Valve Regulated meaning they don't off gas unless under very unusual circumstances, like a direct short?

The Concorde battery, the Aviation sister to Lifeline batteries is a Valve Regulated, Recombinent Gas Sealed Lead Acid Battery, I assume the Lifeline is too, and I would hope most AGM batteries?
In other words under normal operation, I don't think there is anything to vent?

[Suijin]

I just built a "box" for my four AGMs, and it's really just a heavy duty tray. 3/4" plywood bottom, 1x2" hardwood lip around the edge, glued and screwed and coated the whole thing with epoxy. I routed a shallow channel along the middle of the bottom for a ratchet strap with stainless ratchet that holds them all down. Added 3/8" spacer strips between the batteries to give them some breathing room, and bolted the whole thing down on the supporting shelf. The channel for the strap is so I can replace it without having to unbolt the whole thing.

There's no need to build a whole full vertical box for AGMs. Your primary concern should be that they are secure and can dissipate heat.

If it would work for you, I have four Moeller group 31 battery brackets that I bought but could not use. I ended up moving a dedicated start 31 to the house bank and adding a smaller start, so did not have room for the brackets. I'd send you the whole lot for $40.

[Mikado]

Originally Posted by Maine Sail

There is no requirement to build an acid containment box for AGM batteries. They do need ventilation, and proper hold downs, but do not need a box.

Main Sail is correct. No need for a box, just proper hold downs.

AGM's are designed to be stored in any direction. Mine are actually on their side.

I recently requested a Coast Guard inspection. I asked them to take a look at my battery storage to make sure there was not an issue. Everything checked out 100%

[Cabo Jim]

One of my boat projects this year will be to install a bilge blower to my battery box to turn on while charging and dissipate heat. In the past I experienced a "Thermal runaway" on my 5 AGM house batteries, probably caused by an internal short in one of the batteries . When I shutdown the charger and opened the battery box I could not touch the batteries. This was the most frightening thing I have ever experienced on my boat. Plan for the worst and hope for the best.

[Delancey]

My "box" is first and foremost a structure to hold the batteries secure. It bridges two longitudinal bulkheads beneath the cockpit which bear the load.

Making it into a box per Nigel Calder's recommendation would be possible but seems contrary to providing ventilation against heat building up, hence my question. I think it will still have the lid I was planning on putting on it to function as a battery hold down and to protect the terminals but will also provide plenty of holes for airflow.

Thanks for the feedback!

[Kokanee]

I just have 1" holes along the top sides of mine. I considered holes at the bottom as well. It would increase air circulation and therefore dissapate heat better. But in a flooding situation , the battery terminals would be under water slightly earlier than without the vent holes in the bottom. And as others mentioned, if you ever change back to standard L/A batteries, you wouldn't want the vent holes in the bottom.

Yes - I pondered the question as well for too long. In the end - it doesn't really matter. Secure them down well and protect them from being shorted out, and install a heat sensor for your charger.

[ranger58sb]

Originally Posted by Maine Sail

There is no requirement to build an acid containment box for AGM batteries. They do need ventilation, and proper hold downs, but do not need a box.

Originally Posted by a64pilot

I may be corrected but I'd like to have an inch or so around each battery if possible and I too doubt ventilation will be an issue unless you try to seal the lid, it doesn't take much to ventilate the box.

If batteries are in a box, is it OK if they're so close they're touching?

I'm considering a couple of Noco commercial boxes for two pairs of 6V AGMs. https://no.co/hm426

Internal dimensions make it look like Lifeline GPL-4CTs (for example) would be a snug fit.

-Chris

[leftbrainstuff]

Originally Posted by Stu Jackson

Dumb idea. Vent the "compartment" that holds the boxes and you're done. It's almost an "urban myth" about battery fumes anyway, but venting the area is always helpful.

+1

Even when modern lead acid batteries are bubbling vigorously during charging they vent little in the way of noxious fumes.

I spent several weeks convincing Australia's largest Naval build that their mult million dollar battery charging facility was unwarranted.

Some bright spark, visiting online blogs reading posts from idiots shorting batteries with wrenches, decided agm batteries were going to explode and kill naval staff.

To combat his ignorance I conducted battery abuse tests and completed some modelling to show how insignificant hydrogen outgassing is.

The real issue is electrolyte spitting and condensation from over charging and equalizing of flooded lead acid batteries. AGMs are quite benign.

Don't cut holes in the bottom. Vent the tops if you want. Keep the batteries clean, the terminals greased and treat them right.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app

[StuM]

FWIW, my AGMs aren't in a box, they are just secured with tied down straps. This allows much better ventilation.

(It also makes handling them much easier when it finally becomes time to replace them.)

[robbievardon]

I was sailing single handed 72 footer in an area unknown to me with the weather degenerating from force 5/6 to storm 11 through what turned out to be an area which produced sudden and extremely large waves. I had been contacted by the Coastguard on the radio, who advised of the danger but too late for me to avoid the area. Having faced large waves on many occasions, I was not too worried until a huge wave reared up and broke over the boat virtually rolling it over at which point the radio went dead. I doubt if it was more than 2 minutes later that a helicopter arrived overhead, much to my relief and after some hand signals I continued on and the helicopter returned to base. The point of the story is, secure your batteries as a priority. secure your ballast as loose chunks can cause a lot of damage. Despite checking the weather forecast before leaving port which suggested maximum force 8 gale which normally would not be a problem, I was nearly a statistic along with the other crews of the Fastnet race who did not make it.

[Delancey]

Originally Posted by leftbrainstuff

+1

Even when modern lead acid batteries are bubbling vigorously during charging they vent little in the way of noxious fumes.

As mentioned my interest in venting is to dissipate heat, not to vent noxious fumes.

Originally Posted by leftbrainstuff

Don't cut holes in the bottom

Per Maine Sail acid containment is not required for a AGMs so why not cut holes in the bottom to aid in ventilation? Surely you understand when hot air rises it needs to be replaced?

[hzcruiser]

Originally Posted by ranger42c

If batteries are in a box, is it OK if they're so close they're touching?

I'm considering a couple of Noco commercial boxes for two pairs of 6V AGMs. https://no.co/hm426

Internal dimensions make it look like Lifeline GPL-4CTs (for example) would be a snug fit.

-Chris

My old lead acid (LA) and the newer AGMs are touching, even slightly compressed by the straps and hold-down bar I'm using. However, if you're really concerned about heat build-up and really think ventilation is crucial to prevent some sort of over heating, you cannot have them touch and also might want to install a thermometer with an alarm to let you know something is wrong.

The new LFPs I'm putting in even need to be compressed, according to the manufacturer, to prevent them from swelling under normal conditions.

I've had smaller LAs swell while sitting on a shelf for years, not connected to anything. Go figure.