Does anyone have experience or comments, good or bad, about AGM batteries?

Michael Rowe

Subject: TWL: AGM Batteries

Does anyone have experience or comments, good or bad, about AGM batteries?

Michael Rowe

I take this verbatim from Powerboat Reports, September, 1999. This came up
while searching for information on portable jump start power packs.

Sealed lead acid valve-regulated batteries in general, and the Absorbed
Glass Mat (AGM) battery and its hybrid variants in particular, are different
animals (from wet cell batteries). Instead of lead compound plates with acid
and water mixtures (electrolyte) sloshing around, a thick electrolyte paste
is applied to the plates. (This is why you can use these batteries upside
down.) Some chemical substitutions in these sealed cells dramatically
improve resistance to self-discharge, and just enough liquid acid is
integrated into the paste to provide for peak efficiency. If you broke open
a valve-regulated sealed cell, liquid would not pour out (but the mix would
still be caustic). Instead of losing electrolyte during charging, the cells
are under slight pressure (controlled by valves that can release under
extremes) and charging gases are forced to recombine back to usable
chemicals. The close proximity of lead to electrolyte and tight plate
spacing make for extremely low internal resistance and greater efficiency in
energy discharge.
Rather than go into more detail than necessary, suffice to say that the
AGM is charactorized by extremely low self-discharge and extremely high
controlled discharge rates.
AGM manufacturers list cycle life on the order of 500 to 1,000 cycles,
which starts to border on "too good to be true".  *******

Also mentioned in this article is a brand new (1999) technology called "thin
film" which is supposed to be even better than AGM chemistry. Bolder
Technologies in Golden, CO is a maker of thin film batteries.
A call to Bolder Tech revealed they don't have one yet that will start a
diesel, but the portable marine model they have will start an eight cylinder
gasoline engine. It weighs all of 5 pounds. www.boldertmf.com

Zeke Anderson
Texas Cookin'
Rockport TX

A few other aspects of AGM batteries are worth noting.

AGM batteries can withstand freezing.

AGM batteries have a high recharge rate. Unlike flooded or gel batteries
where you can only charge the batteries 20-40% of their amp-hour capacity,
AGM batteries can take 70%+. You can also lengthen the amount of time the
charger is in the bulk stage. If you have a high amp charging source, that
can be very handy. I have a DC genset that can put out 220+ amps 24vdc just
for this purpose.

AGM batteries can be discharged to 80% without harm, compared to 50% for gel
and flooded batteries. That gives you more usable amp-hours in the same
sized battery. However, depending on the battery, at a 80% discharge you
might get 1200 cycles, but at a 25% discharge you might get more like 2500
cycles. So while there is no damage, there is a cost. But there is also a
cost to buying a whole bunch of batteries and storing them in your small
boat.

Speaking of cost, they are more expensive.

Also, AGM batteries have a very low discharge rate. If you leave them for a
month without hooking them up to a charger, it's no problem. "Loss of charge
due to self-discharge is 3 to 10 times better than with conventional gelled,
and 5 to 50 times less than with flooded batteries."

I have them in my current boat and am putting them into my next boat.

Mike Harrington
M/V Meander
Friday Harbor, WA

http://www.hollowbox.net/meander

Michael Rowe asked, "Does anyone have experience or comments, good or bad,
about AGM batteries?"

Summary: (1) AGM are the best thing on the market and Gel Cells are obsolete
junk! (2) Make sure your batteries are "recombinant"!! (3) Ventilate the
battery compartment while charging!!!

We use Hawker Genesis AGM on the Phantom Boat.
http://www.hepi.com/genesis.htm because their high discharge rate supports
the 550 Amp requirements of the 30mm cannon. I also liked the safety of the
spill proof AGM especially since I was selecting batteries for the boat of
the company that determines my annual pay raise :_)>

The best informed and most accurate tutorial on marine batteries is
http://www.redbeardyachtsystems.com/Marine%20Battery%20Facts.htm

Now I am going to get on my soap box. I can't help myself, I have had too
many ordnance safety courses.

It is very important to select a battery with "recombinant" technology. The
recombining of Hydrogen and Oxygen is typically 99+%, so almost very little
water is lost and more importantly very little hydrogen gas is emitted
during charging. Note all batteries will emit some hydrogen gas when
charging and the faster you charge the more they emit. This means that
unless you provide good ventilation during charging you can have a
combustible mixture which only lacks an ignition source to explode. If my
memory serves me correctly, Hydrogen gas is combustible with air in mixture
ratios of 5% to 95%. We keep out batteries in a sealed battery box and
provide >20:1 ventilation flow rate and route the exhaust overboard (we also
blow air into the box as opposed to sucking air through the box so the
blower does not need to be explosion proof, which means it will not create
sparks that would cause an explosion). This assures that there is never a
combustible mixture anywhere on board. If you are too cheap to get
"recombinant" batteries, at least buy Hydrocaps. Hydrocaps reduce water loss
and hydrogen gas emission by up to 95%.

Slight pause while I get off soap box.

Nonexplosively yours;
Mike Schooley
...

You make an excellent case that boats having Mark 38 Gun mounts, older
submarines and those platforms with giatronic boxes have had problems with
hydrogen explosions - though the case of the giatronic boxes sounds like
there may have been other factors.

I think I gave you that point a while ago.  I think industrial users need to
be aware of the problem and take steps to control it.

I am not mixing up thermal versus hydrogen.  I am however aware of thermal
explosions.  I am not aware of hydrogen explosions. In recreational boats
that is.

I have no objection to recombinant technology.  There is in fact a large
push to use hydrocaps on conventional batteries for this purpose.

Your new batteries may well sustain a couple of thousand amps.  How about
when they are 4 years old?  Note that the thermal load of a 1000amp plus
load is still pretty severe.  Something is going to give pretty quick.  I am
the proud owner of a screwdriver with a piece missing an a 1 inch sag.  I
don't think the battery blew in that case either but I would not replicate
the experiment.

A quick search of the first ten pages of your Google search yielded much
information on how to win at Indiana Jones and no information on actual
incidents, any more statistics, of hydrogen explosion on boats.

The crucial issue here is, I think, the criteria for battery selection.  You
are making it a significant safety issue.  I doubt that.  I would argue that
any big sailboat or other vessel capable of surviving a roll should use some
version of the sealed technology.  They should also have provisions to avoid
escape of fuel and sewage.  I get a little more open on a coastal vessel
that would never be exposed to that level of sea. Then we get into the cost
tradeoff between brute deep cycles and the more exotic alternatives.  Unless
your safety case can be made it is unlikely that AGM or gels make any sense
in that application.

I know you feel passionately about the issue - but do you have any data to
justify your passion?

Jim

Jim Donohue wrote, "I'll bite.  How many Hydrogen explosions that damaged
boats do you know of?"

How do you know boat explosions are not due to poorly vented batteries?

The US Navy has experienced at least 28 explosions in the battery box on the
Mk-38 gun mounts over a 12 year period out of 400 installed gun mounts.

"I am sure it is possible but it appears that hydrogen explosions are
generally nuisances - not big deals."

The Mk-38 gun mounts that I referred to earlier have been known to hurl
their 45 lb battery box door up to 175 yards, but this is only a nuisance
(unless you happen to be standing in front of it).

According to http://nt.the-fishing-network.com/magazine/v01/n08/jf-01081.htm
A battery undergoing charging releases considerable amounts of explosive
hydrogen gas and a battery that is being overcharged also has the potential
to become quite hot. Under the right conditions this can lead to a violent
explosion and the possibility of serious damage, fire and personal injury.
Proper ventilation is a must when charging, especially if your batteries are
in a confined compartment within your boat.

According to http://www.mms.gov/incidents/expl96.htm An accident occurred
February 15, 1996 - on board TOTAL of the Minatome Corporation. Remarks:
"Platform operators were sitting in front of the operator's desk located in
the southeast corner of the living quarters at approximately 0530 hours when
the giatronic box exploded. It is believed that the explosion occurred due
to the ignition of a possible chemical leakage and build-up of hydrogen from
a 12Vdc/55AH sealed battery inside the airtight-sealed giatronic box.
Following the explosion, the battery, estimated to be approximately 10
pounds in weight, fell from the shattered giatronic box onto an operator's
lower back. He and a coworker immediately exited the east doorway of the
living quarters following the explosion. Both returned to the area of the
explosion within minutes, and an investigation revealed that damage was
limited to the giantronic box and no additional fire damage was evident."

According to http://www.hazegray.org/navhist/eternal.htm the following
submarines have been lost due to battery explosions.
USS F4              (SS-23)            25 Mar 1915            21 Lost
Battery Explosion off Honolulu
USS COCHINO        (SS-345)            26 Aug 1949            1 Lost
Battery Explosion off Norway
and the following accident resulted in loss of life
USS S49            (SS-160)            04 Apr 1926            4 Lost
Battery Explosion, SubBase New London, Boat survived

I am sure that you are going to point out that these are submarines and not
pleasure boats, however the point is that a hydrogen gas explosion are more
than a nuisance.

"I can find a number of electrically driven battery explosions - but they
would be far worse on an AGM with its ability to pump large, low impedance
current into a fault."

You are mixing two different types of explosions. Internal and external. I
was talking about external explosions.

Internal explosions are caused by either thermodynamic, pressure or chemical
reactions.

Thermodynamic explosions are caused when a high discharge rate is combined
with high electrical resistance generating a very high heat load. This
causes the electrolyte to boil producing steam. Explosions occur when the
steam production rate exceeds the battery venting capacity. Batteries that
are designed for high discharge rates are less likely to suffer an explosion
that batteries that are designed for only low discharge rates. The AGM
batteries that we use on the PHANTOM have a low internal resistance, so high
discharge rates produce very little internal heating. They have been tested
and proven not to explode or suffer appreciable damage or loss of capacity
when directly shorted. The short circuit current is 2,100 AMPS under normal
conditions.

Pressure explosions are caused when the hydrogen and oxygen gas builds up
inside the battery and over pressurizes the battery. Over pressurizing is
mainly an issue with Gel Cells because the gas can not escape from the gel
fast enough. This is why Gel Cell batteries have low charge rates.

Chemical reactions occur then the hydrogen and oxygen are ignited inside the
battery. This is usually caused when the electrolyte low, exposing the
plates (only an issue on flooded batteries) and they are being over charged.

"So where is this data base that causes you to recommend AGM to avoid
explosions?"

Unfortunately, unless their is a very careful accident investigation, it is
difficult to distinguish a battery explosion from a fuel explosion when the
battery bank is in the engine compartment. These investigations are
sometimes hampered by the evidence being scattered over a large area of the
ocean bottom. In addition, if the accident occurs during a voyage, the cause
and the fact that their was an explosion may never be known.

If you read my original post you will see I recommend recombinant batteries
(some flooded batteries have recombinant features, they are generally
referred to as "maintenance free" because they have a lower electrolyte loss
rate) because they reduce hydrogen gas emissions by a factor of 100:1 over
conventional batteries. If you can't afford recombinant batteries get
hydrocaps. They reduce the gas emissions by 20:1.

The important thing is to make sure you vent your battery box to avoid the
nuisance of a battery box explosion. Note: all batteries produce some
hydrogen gas when being charged (despite what West Marine says
http://www.westmarine.com/webapp/commerce/command/ExecMacro/west_advisor.d2w
/show_advisor?fn=459.htm) some just produce a lot less than others.

If you still don't believe me go to Google.com. Search on +battery +venting.
You will find 11,500 references. Add +hydrogen and you will get 2,520. Add
+explosion and you will get 970. Add +boat and you will get 168. Or go to
your battery manufacturers web page and read their safety precautions.

Verbosely yours;
Mike Schooley

OK, the next person who is blown-up in a hydrogen gas explosion from a
battery, post to the list and tell us all about it.

Here are my points:
1 If price is no object, AGM batteries are the best thing available.
2 When you do your price trade-off, take the higher life and higher cost of
AGM batteries into account.
3 If you select flooded deep-cell batteries, try and get recombinant
batteries or hydrocaps.
4 Make sure your battery box is ventilated.

I'm not saying anyone needs to replace their current batteries with AGM, or
that AGM is the right choice for everyone. My intention was only to point
out the advantage of AGM batteries. About 5 replies ago somebody asked about
AGM batteries, so I did a cranial dump for what it is worth.

Returning to lurker mode.

Quietly yours;
Mike Schooley