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Author Topic:   AGM Battery: Need for Battery Box
JTC posted 04-02-2011 11:45 AM ET (US)   Profile for JTC   Send Email to JTC  
I've heard conflicting advice as to whether a battery box is needed for AGM batteries. My [Boston Whaler Conquest 28] batteries are not that high above the water line--they are mounted in the Euro-transom--I was thinking that battery boxes would provide some amount of air-pocket protection if I ever got swamped. I've always assumed that the little grated vents they have on the top of the battery box are small enough so that surface tension would not allow air to leak out of them if the box were submerged. Is that actually the case?

Then again I have a high water alarm and three bilge pumps, so I would have had to take on quite a lot of water before it would matter--enough to fill my entire bilge, plus most of the cabin. Any opinions? I know that a battery that is completely submerged in saltwater will continue to work, but that quite a bit of current will discharge through the water, so the battery will not last long.


weekendwarrior posted 04-02-2011 01:06 PM ET (US)     Profile for weekendwarrior  Send Email to weekendwarrior     
A battery box is a must. It will protect the battery from puncture and wear, protects the terminals from accidental shorts, protects the connections from some exposure to the elements, and water sloshing in the bilge. Most boxes will definitely fill up if submerged.
jimh posted 04-02-2011 06:45 PM ET (US)     Profile for jimh  Send Email to jimh     
I don't see any reason to have a battery box with an AGM battery, other than to keep the electrical connections protected from contact. If the electrical connections on the battery can be covered with insulating boots so that there is no risk of anything shorting the battery, I'd be comfortable not having an AGM battery in a plastic box.

As for something damaging an AGM battery by penetrating its case, you better look around your boat and the area where the battery is located more carefully. If you have something loose that could bust the case on a battery, you've got a problem. Whatever is going to bust through a battery case is going to do a lot of damage to the gel coat of your boat.

The OEM battery boxes from older Boston Whaler factory installations have significant venting. I do not think they will maintain a pocket of air in them if submerged.

Chuck Tribolet posted 04-02-2011 09:30 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
I don't think those vents would keep water out. It's easy
enough to test - take the lid off, fill the kitchen sink
with water, submerge the lid.

And I thought there was some USCG or ABYC requirement for
battery boxes.

And why would an AGM battery be different than a wet plate


jimh posted 04-02-2011 09:53 PM ET (US)     Profile for jimh  Send Email to jimh     
I have to add that I am thinking of a battery already in a shelter like a center console or under the aft deck. If the battery is in the splash well, then I'd use a battery box.
kglinz posted 04-02-2011 10:47 PM ET (US)     Profile for kglinz  Send Email to kglinz     
I run five AGMs. Three are in boxes, two are not. The requirement for Battery mounting is.... sid=c273c77bd32008bf4d57f3b640e4dd66&rgn=div8&view=text&node=33:
davej14 posted 04-03-2011 01:46 AM ET (US)     Profile for davej14  Send Email to davej14     
Since AGM batteries don't require a vented battery box, you should be able to seal up the vents in the top of the box. This would give you a bit of protection if the area became temporarily flooded.
number9 posted 04-03-2011 05:22 AM ET (US)     Profile for number9  Send Email to number9     
Filling up the vents in top of box...if your box is exposed to H20 from above or splash fill them in.

Looking at regs. not too long ago it seems those top vents may be just be the there for mfg. liability not a ventilation requirement.

They appeared w/o any reg. changes and can do more harm than good by allowing water intrusion if not in a covered area.

Duh...the gas that sometimes needs to escape goes out where the cables come in and all the other non-sealed ares.

Wouldn't go as far as others as to suggest going sans a battery box. The box is for protection of your battery physically, environmentally, corrosively, electrically and possibly esthetically.

Just think about allowing room for future use of a battery box while doing your modification etc. You or the next owner of your boat may one day choose a non AGM. Cost or availability.

[Speculated about effects of natural disasters on supply of manufactured materials. Please use the concurrent discussion on precisely that topic.--jimh]

jimh posted 04-03-2011 07:53 AM ET (US)     Profile for jimh  Send Email to jimh     
kglinz--Thank you for the link to the applicable federal regulation governing battery mounting. I did not see any mention of a mandatory use of a battery box in the cited regulations.
jimh posted 04-03-2011 08:01 AM ET (US)     Profile for jimh  Send Email to jimh     
The most significant differences between an AGM battery and a flooded-cell battery in terms of the need for an enclosing container are:

--the AGM battery will not release liquid acid if the battery orientation changes or if the case is punctured; and,

--the AGM battery will not tend to vent corrosive fumes during normal charging. A flooded-cell battery shouldn't be venting fumes, either, during normal charging, but it could if over-charged. An AGM can vent fumes, too, if over-charged and too much internal pressure is built up.

JTC posted 04-03-2011 03:32 PM ET (US)     Profile for JTC  Send Email to JTC     
Thanks for all the input.

On the 1999 28 Conquest, the transom (where the batteries are located) is basically an integral bracket that protrudes past the end of the "real" hull - this is the so-called "notched hull" from that era. So the batteries are on a protected shelf, at or slightly above the waterline and perhaps 2 feet above the bottom of the bilge. I don't think they would be easily splashed or accidentally contacted.

I'll take some pictures when I'm next on my boat (not for weeks) but my new AGM batteries which are not currently in boxes seem to have one advantage: I think they will be strapped down much more securely in the sense that they can't wiggle around inside a box.

anthonylisske posted 04-03-2011 08:04 PM ET (US)     Profile for anthonylisske  Send Email to anthonylisske     
FWIW, I have two AGMs in my console and do not have them in boxes. I mounted them with battery brackets directly to the floor. ( I cut a hole in the floor of the console, so the battery tops protrude into the console)

It has worked great.

Be well

bluewaterpirate posted 04-04-2011 09:02 AM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
Have two AGM's (Sears Platinum & Odyssey). I have the Odyssey in a battery box (cleaner install and the Sears in a battery tray. I have alot of space under my helm area on my 210 Ventura (I can sit in there and work). Two%20of%20a%20Kind%20Electronic%20and%20Fishing%20Upgrades/6-1. jpg?t=1301922049


bluewaterpirate posted 04-04-2011 09:15 AM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
I use three straps on the Oddyssey one to keep it secure in the box and two to secure the battery box to the deck. The reason I do this is I get a lot of motion running in the offshore. Batteries%20545%20BEP%20716/Odessey2.jpg?t=1301922576 Batteries%20545%20BEP%20716/Odessey4.jpg?t=1301922778


Basshole posted 04-10-2011 04:18 AM ET (US)     Profile for Basshole  Send Email to Basshole     
Tom, I really wish the wiring on my boat looked as tidy as yours! Nice work! I am almost inspired to redo mine after seeing your pics.

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