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Old 16-02-2010, 18:11   #1
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Is My Battery Bank Shot!

Have a 12V 800AH (approx) house battery setup (4x4D AGM Deka batteries), only 10 months old (new boat) attached to a Xantrax 40amp charger. Think the charger took a hike recently; not working properly...never a deep charge and output doesn't keep up with loads, waiting for dealer to swap out charger.

Now batteries are acting funny...

After a week of poor charging (charger floats but doesn't deep charge) voltage is 13.2V (no loads). Shut off charger and voltage drops to 12.8V after 30min and holds.

20 amp load placed (charger off) and voltage slowly drops to 11.9V, occurs after 5 min and never bounces back.

Question is...
Are batteries still good and just need a deep charge?
or...
Are batteries shot because of a faulty Xantrax charger?

Your comments are greatly appreciated!
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Old 16-02-2010, 19:44   #2
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They shouldn't be going to 11.9 after just 5 minutes. That's not good. I'd suggest getting a load tester and check each battery independently. Of course, you need to get the charger swapped out and then fully charge them.

Could they have been damaged from a faulty charger? You bet. Overcharging an AGM will kill them very effectively and they don't come back.

Good luck.

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Old 16-02-2010, 19:50   #3
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there's a good chance that you've got a single bad battery that's causing the entire bank to perform poorly. disconnect and test again.
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Old 17-02-2010, 05:17   #4
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I had a similar situation with a much smaller set up. I had a Xantrex True Charge 20 and 3 Group 31 Surette batteries. On arriving at the boat one day I noticed a strong sulfer smell throughout the boat, The batteries were overcharged and wouldn't power my 12 volt fridge for more than a couple of hours. I wrote to Xantrex and also send them a copy of my 1 year old (2) batteries invoice. They replaced the charger under warranty and sent me a cheque for $ 540 for 2 of the batteries. Great service at the time in 2001. The replacement charger lasted about 4 seasons (6 months/season). I replaced the charger with a Pro Mariner 1230i 4 years ago, no problems as of yet.
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Old 17-02-2010, 06:30   #5
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I think that your root cause problem is an undersized battery charger that has had to work too hard in an attempt to charge your AGMs. Thus, the overworked battery charger failed. The battery charger you cited provides only 0.05C charging capacity where C = bank capacity. AGMs can generally accept a charging rate up to C.

The TrueCharge 40+ has slide switches to determine charging mode, battery type and temperature setting. Were these settings correct for your AGMs and the bank temperature?

On the battery side, a flaky acting battery charge could lead to inadequately charged AGMs and lead to their demise due to plate sulfation.

Heat is one of the biggest killer of batteries. To mitigate the affect of heat on a battery bank, adequate cooling around each battery, solid wiring, temperature compensation sensor on the most representative battery in the bank, etc. would have to be in place.
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Old 17-02-2010, 06:57   #6
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i found the same sulphur smell a few summers ago and attributed it to a series of brownouts that may have confused the charger. the batteries were OK but i did not get new ones from xantrex!!
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Old 17-02-2010, 07:04   #7
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My research although debatable is to use Trojan #145s 6Volt batteries in series.(Lighter and easier to handle) Check your charging rate as it is recomeded to be 30 Amps per Hour max to get the most out of your batteries. This research is over a 30 year span of sailboat batterie usage. AGMs just wont last as long.
Call Trogan Co. & let them known your daily need of storage, you probably will need to double that need to afford proper charging & storage if not tripple it.
I hope this is of some help.
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Old 11-03-2010, 05:13   #8
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I agree with Charlie--double the size of the replacement charger. You should not wait around to get the battery bank recharged, as they will sulfate in their current deep discharge state.
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Old 11-03-2010, 07:41   #9
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When I overcharge my flooded cell batteries it is called EQUALIZING. Just another case to reinforce the idea that while AGM's have some desirable qualities, the down side has become apparent. This is the third case of early death of AGM's I have seen in the past month.
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Old 11-03-2010, 15:20   #10
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Jentine-Not to put to fine a point on it, but the OP did not mention "overcharging". Quite the contrary, it is my opinion that he severely undercharged his batteries which lead to sulfation and premature failure. This condition will also occur with FLA batteries if you chronically undercharge them. The difference being that FLAs can be equalized whereas only some AGMs can be.
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Old 11-03-2010, 15:36   #11
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While he may have undercharged the batteries, I think it unlikely that sulfation alone could explain what he's seeing. Yes, capacity could be reduced -- even severely -- through sulfation, but with an 800AH bank the 20A load is minimal and should NOT draw the bank down to 11.9 after only 5 minutes, and remain there after the load is removed.

First thing to do, as mentioned above by ID, is to check each battery individually with a good voltmeter. Do this when you're seeing the 11.9 volts or so. You could well have a single bad battery.

You won't know about the damage done thru undercharging until you do a good load test on each battery. A pretty good proxy to use is the Midtronics testers...see if some one has one. The best way to do a load test, though, is to charge them up fully, then apply a known load guaged to the 20-hour rating of the battery. See how long it takes to pull the voltage down to 10.5.

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Old 08-04-2010, 00:40   #12
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Donradcliffe You are quite right.....
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