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Old 15-05-2010, 07:15   #1
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AGM Battery Bank Failure - Help !

I have a 800ah battery bank that is maintained by solar panels and a trace C40 charge controller.

i have two 245ah, 1 198ah and 1 90ah in the bank

Last time i came to the boat the battery bank was very low and the boat barely started. Running the engine for hours did not help so I tested each battery and found one bad 245ah unit. i took it out the circuit and now everything appeared to be working, the remaining batteries taking a charge. I use the boat for a week no problems. Now I leave the boat and solar panel on to maintain batteries (as i have for years).

A month later i come back and ALL the batteries are bad. none will hold a charge. when disconnected to test, one measures 9v one 4v one is at 11V but wont hold a charge.

They were all installed 6 years ago.

The solar system is definately putting out a charge.

Is it strange that all the batteries have gone down at the same time ? did the first bad battery ruin the rest ?

Before i buy a new very expensive set of batteries, i want to know if they just reached the end of there life or do i have a charge problem with the solar panels. How would i test it.

i have searched posts but not found any conclusive info.

Any help deeply appreciated. I am stuck in Green Turtle Cay till i figure it out.

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Old 15-05-2010, 07:36   #2
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Hmmmm.... How long do would AGM batteries, or indeed any Lead acid batteries last? It seems like 5-7 years is fairly normal for most. Many get better life when the charging/use regimes are optimized.

Most wisdom suggest that the batteries in a bank contain batteries of not only equivalent voltage and amperage, but that they indeed be the same brand and age. This is largely suggested because of the need to avoid some of the problems you may be encountering. That being that a bad battery may cause the other batteries to be over/undercharged with the results being damage to other batteries in the bank.

Indeed, it has be suggested that AGM batteries are more sensitive to reduced life because of suboptimal charging. Lots of discussion on many other threads.

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Old 15-05-2010, 08:11   #3
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It does sound like you have nothing to complain about having had them for 6 years which is a decent avg lifetime and particularly so given you mixed batteries of substantially different capacity which would only exacerbate the problem.

It is always a good idea that when installing new batteries one also verify the charging system is operating properly lest replacement gets to be an annual exercise.
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Old 15-05-2010, 08:38   #4
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All batteries can be damaged by over or under charging. AGMs need to be fully charged at least once every few weeks.

I agree with other comments about same type and size batteries in the house battery bank. Also about longevity.

Question: does your solar charger system utilize an MPPT or other regulator/controller? If not, in Marsh Harbour it could well be cooking your batteries, causing plates to buckle, short out, and bring an end to useful battery life.

Best to start anew and take care of the new batteries, ensuring that the charging regimes are appropriate.

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Old 15-05-2010, 08:39   #5
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batteries are designed for due cycles and not for time used.. if they have been cycled to the max, they are gone..
Mixing the size of the batteries can have an issue with charging but not in overal life but they will only be charged to capacity of the smallest battery..
could be the batteries themselves, and have spent their life..
For overall life, I have lifeline AGM's of 4d size.. we have 10 of them on board.. all are the same size.. every 6 months we fire up the motor and cook the batteries for 8 hours.. they are charged with solar and wind and have never been on a charger..
After 7 years, they still settle at 12.8 volts which is 100% charge.. 12.2 volts are 50% on the lifeline 4d's and ours have never gone below 12.6 volts..
We expect to get 20 years out of ours and it looks like we're on our way...
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Old 15-05-2010, 09:38   #6
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There are worse places to get stuck than GTC! When my battery bank died last year I was on MOW. I'm hoping that I will actually be able to leave the dock this year.

I cannot comment about what caused your batteries to fail after 6 years. My batteries (one starting, one house) lasted only 3 years, most likely the result of my own neglect. However, you have received some useful advice and comment from the other posters.

One thing I have noticed about batteries in the Abacos is that they are EXPENSIVE! My starting battery, which I replaced last year, cost me twice what I would have paid in the States, or even Nassau. I'm not looking forward to purchasing my house battery this year.

I suggest that if you're headed back to the States, purchase only those batteries you need to get home safely. Complete your battery purchases in the States where you will have any number of manufacturers to choose from, at prices much less than you'll pay in the Abacos.

Good luck!
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Old 15-05-2010, 09:47   #7
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My bank of 6 AGMs died at 7 years... I swapped those (and the two engine start batteries, just in case) via dinghy while at anchor. I don't recommend this. 560 pounds each way!

The event that hastened the demise of mine was the eternally flaky Prosine 2.0. In addition to a deadly failure mode triggered by a glitch of shore power that would result in the unit coming back on but not charging, thus killing the batteries... it decided during one of its crashes that the batteries were actually gel and spontaneously changed the setpoints.

I blame it for shortening the battery life... some were visibly swollen. But they were getting long in the tooth anyway. (And I pulled the Prosine out and replaced it with an Outback.)

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Old 16-05-2010, 18:18   #8

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The Trace C40 appears to be a dedicated solar panel controller. Assuming it is programmed correctly and operating correctly, you still might have a problem from using three very different batteries in the combined bank. If each came from a different vendor, each may actually operate 1/10th of a volt or more off the voltage that the next one needs, due to different battery chemistries. Then there is the matter of the very different capacities, which pretty much ensures that no matter how the charger senses battery voltage, at least one will be overcharged and another always undercharged--killing the batteries.

In that type of mix I'd think six years might just be adequate performance from them, and strongly suggest that when you replace them, you use all one type of battery all from the same lot and source. Meanwhile, this is the time to verify that the charge controller is or isn't working properly. Hook it up to just one battery, use a voltmeter (leave it inline, in volt and amp modes, and check it for longer terms, not just on the spot) and confirm it is controlling maximum voltage properly. And run your fingers and eyes over the rest of the system, inspecting for bad connections, bad cables, or any other physical problems. (That should be a routine inspection every once in a while, anyway.)

Assuming all the batteries are bad--you may be able to beg or borrow something from a local battery supplier, for test purposes, in the interest of giving them your business when you do order the replacements.

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