• Mobile App For Android Now Online!

    Download it here. The app is searchable in the Google Play Store under Sailboat Owners.

    Sorry iPhone/iPad users, we are still waiting on Apple. :(

    Click the X in the upper right corner to make this go away

AGM Batteries - Making The Choice

Feb 6, 1998
11,094
Canadian Sailcraft 36T Casco Bay, ME
[


Thought these Duracel AGM's were same as West marine dual purpose batteries, made by East Penn.
I have the West Marine AGMs; 5 1/2 years old and still good. That's after running them down below 40-50% at least 2 or 3 times.
They are the same batteries, but East Penn's AGM's are not the best choice for a "cycling" AGM battery. East Penn's GEL batteries are a tremendous quality cycling battery and their Golf Car and industrial deep cycle batteries are also good. Their AGM's are okay for starting but their are much better choices for cycling batteries.

Again, I would urge anyone considering AGM's, that will actually get used for deep cycling, and PSOC use, (partial state of charge) to read the Practical Sailor testing. The differences in how AGM batteries actually hold up to cyclic PSOC abuse is like apples and oranges.

Practical Sailor May 2015
Practical Sailor August 2015
 
  • Like
Likes: BigEasy
Jun 21, 2004
1,292
Beneteau 343 Slidell, LA
Thanks Maine for the excellent analysis and references. I had gel cells on a previous boat and got good service from them. Five years ago When I was replacing flooded batteries on my new to me boat, I thought that AGMs would be a step up in reliability & service. Was also concerned about less gassing as the batteries are located in an unvented compartment under the aft berth as configured by Beneteau. Will have to reconsider when I need to replace the present batteries. I really don't want to spend $1800+ for a high quality AGM bank that consists of 4 group 31 house bank and a group 27 starter battery. Might have to reconsider gels again.
 
Jun 14, 2010
1,140
Quorning Dragonfly 1200 home
This is all great info. I’m guilty of murdering batteries also, and after one expensive experience of murdering AGMs after 3 years, decided to buy Kirkland FLA deep cycle batts at Costco. They seem to last about 4-5 years for me. My boat uses 5 group 24 batts which are approximately $70 each (last time, and might have been less after core refunds)
My boat is on a mooring, and I often leave the fridge running 24/7 which works out fine on clear days, the solar array keeps up - but not if we have overcast weather which results in PSOC (often weeks at a time). If I know I’ll be away for 5 days + I shut off the fridge and bring anything home that would spoil. Then I come back to 100% SOC.
 
Nov 26, 2008
1,909
Endeavour 42 Cruisin
Was also concerned about less gassing as the batteries are located in an unvented compartment under the aft berth as configured by Beneteau.
Is this a real concern? I have a 750 a/h wet cell bank (used to be 900 a/h) under my bed. Been living aboard for over 6 years full time. Other than the extra eye that has grown on my forehead, I've seen no issues. This is an Endeavour 42 built in 1985. There are thousands and thousands of boats with similar configs and I've only seen theoretical issues raised. Granted, if the bank goes boom, I'll finally get some action in bed. Otherwise...
Is this much ado about nothing?
 
Jun 14, 2010
1,140
Quorning Dragonfly 1200 home
Is this a real concern? I have a 750 a/h wet cell bank (used to be 900 a/h) under my bed. Been living aboard for over 6 years full time. Other than the extra eye that has grown on my forehead, I've seen no issues. This is an Endeavour 42 built in 1985. There are thousands and thousands of boats with similar configs and I've only seen theoretical issues raised. Granted, if the bank goes boom, I'll finally get some action in bed. Otherwise...
Is this much ado about nothing?
Yes hydrogen gas is HIGHLY explosive. Enough concentration, and a spark, then boom.

Unlike LP or CNG, there is no odor. It rises, so the vents need to allow it to rise.
 
Nov 26, 2008
1,909
Endeavour 42 Cruisin
"Enough concentration". How much is too much?

How many 'booms' have been reported from battery off-gassing (not from plate defects)?

Are there setups with absolutely zero ventilation?
 
Jun 14, 2010
1,140
Quorning Dragonfly 1200 home
"Enough concentration". How much is too much?

How many 'booms' have been reported from battery off-gassing (not from plate defects)?

Are there setups with absolutely zero ventilation?
Google the explosive concentration. I think your situation all depends on how aggressively your system can charge your battery bank, and that’s what causes outgassing. I don’t know how to define “safe”.
 
Nov 14, 2013
178
Catalina 50 Seattle
The lower limit of flammability is 4% concentration, which is a lot. Hydrogen gas is much lighter than air and a very small molecule that's difficult to contain. Unless you put the batteries in a tightly sealed compartment, it's virtually impossible to achieve the minimum flammability concentration.
 
Nov 26, 2008
1,909
Endeavour 42 Cruisin
The lower limit of flammability is 4% concentration, which is a lot. Hydrogen gas is much lighter than air and a very small molecule that's difficult to contain. Unless you put the batteries in a tightly sealed compartment, it's virtually impossible to achieve the minimum flammability concentration.
Which is likely why we don't hear about it.
usually the discussion revolves around corrosion from the gasses and poison for people breathing it.
 

Gunni

.
Mar 16, 2010
5,943
Beneteau 411 Oceanis Annapolis
The concern is that FLA’s gas off, need regular watering and are open vented. Depending on the size of the bank and the load there can be a lot of gassing and acid spew. So people put them in battery boxes to contain the corrosive acid damage while also containing hydrogen gas. On boats a FLA typically gets installed down low, maybe in the bilge. If flooded with sea water those open battery caps will allow the battery to start gassing Chlorine. Plenty of people use FLA and most are just fine. I wouldn’t sleep on top of any battery install.
 
Apr 11, 2018
1
MOODY 33 mk1 Oceana Rain Stonington ME
Big fan of maine sail!

I am wrestling with how to approach my charging. I originally was planing on buying two 6v gulfcart and using my Mitsubishi 50a dumb regulated alt. (from a westerbeke w-27, I believe you are well acquainted) and supplementing with solar to top off at the morring. I live by the saying "keep it simple stuped"

My plans went amiss when I was poking around Mardens and stumbled on a pallet of brand new Exide MC-31 agm-200 for 80 bucks a pop. Ended up buying 3.

Now I have acquired a charging problem along with some batteries.

Being cheap and broke its hard to pull the trigger on 700-900$ on a new alternator and external regulator. And would rather not put that extra demand on my diesel.

Will I hurt the battery bank (overcharge) if i continue with the stalk altinator and instead invested in a 200 or 300 watt solar system to top off the batteries.

I am intending on about 2 week coastal cruising. And i end up motoring a fair amount around the islands of penobscot. will the 50a over charge the batteries if I motor to long?

Im at the point were i may just sell the agms and go back to my original plan with the gulf carts.
 
Feb 6, 1998
11,094
Canadian Sailcraft 36T Casco Bay, ME
Big fan of maine sail!

I am wrestling with how to approach my charging. I originally was planing on buying two 6v gulfcart and using my Mitsubishi 50a dumb regulated alt. (from a westerbeke w-27, I believe you are well acquainted) and supplementing with solar to top off at the morring. I live by the saying "keep it simple stuped"

My plans went amiss when I was poking around Mardens and stumbled on a pallet of brand new Exide MC-31 agm-200 for 80 bucks a pop. Ended up buying 3.

Now I have acquired a charging problem along with some batteries.

Being cheap and broke its hard to pull the trigger on 700-900$ on a new alternator and external regulator. And would rather not put that extra demand on my diesel.

Will I hurt the battery bank (overcharge) if i continue with the stalk altinator and instead invested in a 200 or 300 watt solar system to top off the batteries.

I am intending on about 2 week coastal cruising. And i end up motoring a fair amount around the islands of penobscot. will the 50a over charge the batteries if I motor to long?

Im at the point were i may just sell the agms and go back to my original plan with the gulf carts.
If anything it will under charge your bank during partial state of charge use.. Those Mitsubishi alts have a pretty strong voltage gradient, like the Hitachi's do, and they reduce voltage they heat up making it tough to really charge AGM's adequately.

The batteries were $80 bucks each, and are not a premium deep-cycle AGM, so if you ruin them, not a huge deal. You don't have to spend $700.00+ to get better charging. There are now plenty of options to get into a premium quality Balmar regulator and an externally regulated alternator in the $600.00 range.
 
Jul 29, 2017
169
Catalina 380 Los Angeles
The only explosion of a lead acid battery that I am directly aware of happened to myself when I had an alternator go bad on my car many years ago. The battery boiled out almost entirely. I called AAA for help. I told the driver of the tow vehicle not to attach jumpers but instead bring battery (distilled water) so I could drive the vehicle home, a distance of about 1 mile. Instead he tried to jump a nearly empty battery that promptly went BOOM!!!!!!:banghead:
 
Feb 6, 1998
11,094
Canadian Sailcraft 36T Casco Bay, ME
The only explosion of a lead acid battery that I am directly aware of happened to myself when I had an alternator go bad on my car many years ago. The battery boiled out almost entirely. I called AAA for help. I told the driver of the tow vehicle not to attach jumpers but instead bring battery (distilled water) so I could drive the vehicle home, a distance of about 1 mile. Instead he tried to jump a nearly empty battery that promptly went BOOM!!!!!!:banghead:
This happened a few years ago. Automotive charger on a marine battery. Boat was very heavily damaged by acid & luckily no-one on-board at the time.....

 
Oct 22, 2014
11,131
CAL 35 Cruiser Portland OR, moored EVERETT WA
Why is care needed around batteries? Because the boiling battery is venting Hydrogen Gas.

Hydrogen gas and normal air can ignite at as low as 4% air 96% Hydrogen due to the oxygen in the air and the simplicity and chemical properties of the reaction. Fortunately the hydrogen dissipates quickly. But when captured in an enclosed container then the fun can begin.
 
Aug 13, 2012
519
Catalina 270 Ottawa
Hydrogen gas and normal air can ignite at as low as 4% air 96% Hydrogen
It is the opposite concentration (4% Hydrogen/96% Air).
If we want to split the hair, the 4% concentration can ignite, but for an explosion, you need 18%, which still is pretty low.
 
Oct 22, 2014
11,131
CAL 35 Cruiser Portland OR, moored EVERETT WA
My bad. Sometimes my brain speaks faster then my hands can type...
It is still a an issues to be of concern for boaters particularly when the components Fuel (Hydrogen) Oxidizer (Oxygen) and Ignition source (think about it... electrical spark etc) are potentially present.