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post #1 of 14 Old 09-24-2012 Thread Starter
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Dead AGM bank

New boat for us, 2nd day onboard.

Boat is equipped with 3 battery banks all made up of Grp 31 AGM batteries.

Engine bank is a single battery.
House 1 is two batteries and house 2 is four batteries.

Heart Invertor/Charger

As I poked around I first noticed house 2 was taking a big charge for extended period (14+ v), yet voltage for that bank was down around 10.5 volts with the charger off.

I disconnected the cables and used a meter on each battery in house 2 and found 3 show around 9 volts while the 4th is showing 11.5 volts.

I'm assuming that at least three of the batteries need to be replaced. Frankly I can't afford 3 batteries at the present -- just bought this boat and the other boat hasn't sold yet. If the battery showing 11.5 volts is still good could I use it as the only battery in house 2? Would there be any issue with the charger since there would only be 1 battery in the bank. I must have a house 2 bank because my bilge pump is wired to that bank at the switch.

ALL electrical stuff is magic to me, I can take two wires, a battery and a bulb and make light but that's about the limit of my electrical theory.

What could cause three batteries to go bad?

I'm not sure how "sharp" the former owner was. He left all battery switches on ALL the time thinking the switches needed to be on for the batteries to charge from shorepower. No clue as to how he treated/used/maintained the batteries. He said the batteries are three years old.

Any help appreciated.

Dale

S/V Elnora
Pacific Seacraft "Crealock" 37 #312

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post #2 of 14 Old 09-24-2012
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Re: Dead AGM bank

Dale,

Unfortunately, my friend, it sounds like ALL your batteries need to be replaced. The age of batteries is not a good indicator of their condition. As you may know, it's much more important HOW THE BATTERIES ARE TREATED.

AGMs need to be FULLY CHARGED frequently...at least once a month...in order to live a reasonably long life. They're great for some applications, but for most boaters they are more expensive and more troublesome than necessary. And, they won't last anywhere near as long as good flooded batteries or gelled batteries.

The voltages you're seeing are WAY TOO LOW. An AGM battery which is reasonably well charged and with the charger removed should measure 13+ volts and, after sitting overnite, should measure at least 12.7VDC. I think it's safe to assume that all your batteries are shot. Only way to tell for sure would be to do a true 20-hour load test or check the batteries with a sophisticated (and expensive) internal conductance meter like the Midtronics Series.

That's the bad news.

The good news is that in all likelihood you don't need to spend all that much money for AGMs. Flooded deep-cycle batteries will likely be fine, depending on how you plan to use the boat.

You need to check the output from the battery charger to be sure the voltage is high enough, and it should be a multi-stage "smart" charger, NOT a ferro-resonant automobile charger. Anything else will kill your batteries in a short time.

The best bang-for-the-buck in house batteries are golf-cart size....6-volt batteries...in pairs. Two of them in series will give you 12V, and they have thicker plates and will last longer and take more abuse than will 12V batteries.

If you can provide some more info about your cruising plans, battery charger, etc, maybe we can help you further.

Bill
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post #3 of 14 Old 09-24-2012
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Re: Dead AGM bank

Our AGMs died, all of them at once, with little or no warning. Same kind of voltage you're seeing. They were 5 yrs old.

Luckily we were at an anchorage where we could dinghy in and get at least one replacement battery to get us home.

Stuff happens. Its a boat.
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post #4 of 14 Old 09-24-2012
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Re: Dead AGM bank

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Originally Posted by MMR View Post

Stuff happens. Its a boat.
Not really. Forewarned is forearmed.

AGM Battery Issues (from Maine Sail)
AGM Batteries - Making The Choice - SailboatOwners.com

AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
Darn AGM Batteries - SailboatOwners.com

Stu Jackson, C34, 1986, M25 engine, Rocna 10 (22#)
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post #5 of 14 Old 09-24-2012
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Re: Dead AGM bank

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Originally Posted by MMR View Post
Our AGMs died, all of them at once, with little or no warning. Same kind of voltage you're seeing. They were 5 yrs old.

Luckily we were at an anchorage where we could dinghy in and get at least one replacement battery to get us home.

Stuff happens. Its a boat.
This is a fairly common failure mode for AGM's. I still don't know why they fail like this but this is how it often happens. I suspect an internal shorting failure where with flooded batts it can be more gradual and with AGM it seems to happen more suddenly. One minute they appear to be working fine and the next they just fail catastrophically with little advanced warning...

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post #6 of 14 Old 09-24-2012
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Re: Dead AGM bank

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Originally Posted by Stu Jackson View Post
Not really. Forewarned is forearmed.

AGM Battery Issues (from Maine Sail)
AGM Batteries - Making The Choice - SailboatOwners.com

AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
Darn AGM Batteries - SailboatOwners.com
Yea. We were aware of those issues. Hubby was obsessed about making sure we were always charged - solar at anchor and motoring to charge on the way back into the dock where there was shore power. He monitored the bank charge several times a day when underway and weekly at the dock.

Still. One minute we had power. The next - nada.

Its a boat. We're not doing AGM on the new-to-us Irwin - and making sure we have a power backup plan or two.
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post #7 of 14 Old 09-25-2012
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Re: Dead AGM bank

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Originally Posted by MMR View Post
Yea. We were aware of those issues. Hubby was obsessed about making sure we were always charged - solar at anchor and motoring to charge on the way back into the dock where there was shore power. He monitored the bank charge several times a day when underway and weekly at the dock.

Still. One minute we had power. The next - nada.

Its a boat. We're not doing AGM on the new-to-us Irwin - and making sure we have a power backup plan or two.
Yeah, want she said.
People wonder why we sold the Gemini - ash tray was full, Fridge was empty and the batteries were dead.

Sudden failure sucks, had to pay 160 bucks for a CHEAP starter in St. Micheal's just to limp home.

Lessons learned are opportunities earned.
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post #8 of 14 Old 09-25-2012
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Re: Dead AGM bank

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People wonder why we sold the Gemini - ash tray was full, Fridge was empty and the batteries were dead.
Man, I missed your posts, Chuckles!

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post #9 of 14 Old 09-25-2012 Thread Starter
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Re: Dead AGM bank

More info.

Pulled the batteries out from the bad bank. 3 were showing 7v, the 4th was at 11.5 v. Left the 4th battery in and put it back on the shorepower charger for several hours, as soon as I put a load (bilge pump) on it voltage went to nothing. Two of the low voltage batteries were slightly bulged on the end.

The boat has a Freedom 10 Inverter/Charger. As I looked through the manual I see it can be set for wet cell or gel cell batteries -- no setting for AGM. Could this be an issue?

Dale

S/V Elnora
Pacific Seacraft "Crealock" 37 #312

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post #10 of 14 Old 09-25-2012
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Re: Dead AGM bank

Dale, the answer to your question is "What are the correct charging regimens for AGMs?"

I've found the easiest way to find this is to find an extenral alternator regulator manual. They almost always give the different recommended settings. Try Welcome to Balmar - 2012 and download or read the MC-614 manual, one of the pages has all the setup voltages for the different charging phases (stages).

IIRC, AGMs are quite like regular lead acid batteries.

Also check with your battery manufacturer.

Stu Jackson, C34, 1986, M25 engine, Rocna 10 (22#)
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