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I'd rather be sailing
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Discussion Starter · #1 ·
OK... lots of battery questions for me these days!

We have two 8D AGM's (490AH). We only drain about 150AH to 180AH out of them before we recharge. The most I've ever drained them is 235AH. We charge them through a generator powered Xantrex Inverter/Charger, and monitor the charge on a Xantrex Link 1000. A few weeks ago, when they were drained, we'd see the charge rate at about 60-65amps until they were about 85% charged, and then would see the number dwindle down to about a 25-30 amp charge rate (i.e. they appeared to be charging correctly). Over the past few days, I've noticed that when they are about 70% charged, the charge rate starts "dancing" between 30amps and 50amps - changing every few seconds. There has been no load change on our electrical system (that I'm aware of) during the charging time.

Since there has been a change in the way the batteries charge, I'm trying to figure out if the batteries have started living out their useful lifetime (they are about 5 years old, and now we're liveaboards so charge every day), or if perhaps the charger is starting to fail. Any thoughts on where I should start looking? I'm new to this battery stuff!
 

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Sounds like it might be the batteries getting older but you have one more variable that you haven't mentioned that has significant impact on battery charging.

You are now in a warmer climate.

Temperature does matter. Do you have a temp monitor on your battery charging equipment?
 

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Have you equalized?
Have you topped off to 100% with shore power recently.
Might need to top off overnight and then EQ.
How does the specific gravity look? Even across all cells?
 

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I'd rather be sailing
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Discussion Starter · #4 ·
They are sealed AGM's, so generally you don't have to equalize (from what I understand) and there's no way to measure the specific gravity (as far as I know). We haven't topped off with shore power, but we topped off with generator power a couple of weeks ago. Normally, we bring them to 90%-95% with the generator. Now I'm having trouble even bringing them to 80%.
 

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Discussion Starter · #5 ·
Chuckles - I have to verify if we have a temp sensor. I believe we do. The batteries and the charger, however, are below water line and the air temp around them is generally around 70-75 degrees.
 

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correct, no EQ for AGM

Check the resting voltage about a half hour after charging. See if it's where it should be. Resting voltage is with no drain
 

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Discussion Starter · #7 ·
I don't think I'm going to get anywhere near 90% charge today. They've been charging for 2 hours and are only at 75%. Always fun...
 

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Warm Weather Sailor
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Vero has been known to suck the life out of everything, including batteries. :) On a more serious note your batteries have not been getting a full charge lately as you have to run the charger a very long time to get them right up. I have found that on the hook you end up using the band between 50 and 85% as it just takes too much to bring them up tp 100%. Over time your capacity decreases, I have found Links to be less than accurate (it may just be me). As to the charge fluctuating so greatly have you checked all your connections?
 

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labatt,

I'll throw my $.02 in from my 30+ years in dealing with equipment (albiet not all marine) with group batteries and their maintenance. First, Chuckles is absolutely right, changes in temperature and usage will affect charging system and battery performance. Problems that didn't show themselves before will crop up when you change the environment where they operate. Whenever I encounter an electrical problem (or any problem for that matter) I try to eliminate the easy things first. In my experience, a vast majority of battery charging problems have bad or corroded connections as at least a contributing cause. Not always, but the best place to start. Next, I'll check to see if the monitoring guages on the equipment is telling me what is really happening. A good volt meter will tell you a lot. Take static readings on each battery and then readings while you are charging. These will help check the accuracy of your on-boat guages as well as compare the relative condition of each battery. If one battery shows a significant difference from the others I would suspect a battery problem. Especially if the group has been equalized. The next step would be to check the condition of each battery. The only way I know of to that with your type of sealed batteries is with a carbon-pile load tester. It tests the battery's ability to draw a load and sustain a minimum voltage. The problem is that a good quality tester is quite expensive so your best bet is to take your batteries out and to a shop that has one. Remember that the battery must be fully charged to get accurate test results. One last thing I can think of on the easier side of the ledger...make sure that you don't have something on your boat that is drawing a higher load than it used to. Especially with isolated batteries a changed load may affect one battery differently than another.
 

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Labatt-
"They are sealed AGM's, so generally you don't have to equalize (from what I understand)" You are 100% correct on this. In fact, "every" AGM manufacturer except LifeLine will tell you that attempts to equalize their AGM batteries will ruin them. LifeLine is the exception to the rule, one must presume their batteries are built very differently. (Perhaps simply a more robust case to allow higher pressure internally.)

It sounds like what you are seeing is your charger switching from bulk phase to absorbtion rate, and back and forth between the two. This *might* be appropriate, or it might indicate that whatever usually prevents that kind of back-and-forth switching has broken, i.e. a circuit failure. I would contact the charger maker and ask them what is normal for the circuitry that they are using--because that's the only way to know if this is a problem, or routine for the conditions.
Could be a loose wire on the charge sense lead, which is providing a correct feedback voltage, then heating up, opening up a tad, creating a false reading, and cycling back and forth. So you might want to check all the leads and connections to be sure they are clean and tight, and if it persists, then make that phone call.
 

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The fact that for on AGM's you don't equalize is good and bad. It's good because you don't have to bother with it. However, it's bad because you can't equalize them. You gain convenience, but loose some life span. My guess is that you are seeing the beginning of the end of your batteries.
 

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Discussion Starter · #13 ·
Well, I've traced through MOST of my pre-panel system, pulled connections off, cleaned them and refastened them. Basically, I can charge the batteries (AGM) to 12.75v (70-75%) and then it takes FOREVER (read: not going to happen) for anything higher. When I first start the charger, it only takes a few minutes for them to reach 14.3v and come off bulk charge to "Accept". At bulk, I'm pushing 60+amps into them. At accept, I'm pushing a fluctuating amount, as I should be. Last week I could charge them to almost full in a couple of hours. It seems weird to have such a drastic change in so short a time. BTW - All voltages are read directly off the battery using the voltmeter. The Xantrex does match. I'll have to call Xantrex up and see if they have any suggestions.
 

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Warm Weather Sailor
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labatt,
. The problem is that a good quality tester is quite expensive so your best bet is to take your batteries out and to a shop that has one. Remember that the battery must be fully charged to get accurate test results. .

All excellent advice but some of it is highly impractical when cruising. You can't take the batteries out, you need them. Also you're usually on the hook without shoreside transportation. You might get them right up if you motor for a full day. In the end I have come to grips with living with less than ideal conditions. For example my Link 2000's memory has been corrupted. It will not read my charging or usage on bank #2. Of course this is the house bank. I've followed the manufacturers advice to try and reset. No joy. I'll have to live with it as an expensive volt meter until I lay the boat up at the end of the season in June. In the same way I've come to grips with using only 35% of my bank, that between 50 and 85%. After a little while cruising you get used to living in a less than perfect or textbook environment.
 

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Well, I've traced through MOST of my pre-panel system, pulled connections off, cleaned them and refastened them. Basically, I can charge the batteries (AGM) to 12.75v (70-75%) and then it takes FOREVER (read: not going to happen) for anything higher.
labatt,

That is characteristic symptom of plate sulfation. It can be reversed with an equalization (15-15.5 volt) charge. If your AGMs are Lifelines you should apply an equalization/conditioning charge. Stay with them while equalizing: keep them well vented and put your hand on each battery at least once an hour to check the case temperature. If they begin to feel "hot" ~180-deg. it is time to stop, even if full charge has not been achieved. I brought my set of 3 GPL-4DA Lifelines back from ~76% capacity to full capacity with an equalization charge that lasted 10-Hr. This will be their 6th season of use.

The reason Lifelines may be equalized (the manufacturer recommends a periodic "conditioning" charge) is that they are built with pressure relief valves.

A small amount of hydrogen gas is produced while charging and must be vented or the battery cases will distort and in extreme cases burst. Check with the manufacturer to see if they incorporate PRVs.

Five years of use with infrequent (?) topping off to full capacity is probably the culprit.

Wayne
 

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how about charging one battery at a time, separately. You might have one bad battery in the chain slowing things up.
Or at least disconnect all batteries after charging to check the voltage of each to see if there is consistancy
 

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Wayne-
"The reason Lifelines may be equalized (the manufacturer recommends a periodic "conditioning" charge) is that they are built with pressure relief valves." ALL sealed batteries are built with pressure relief valves, to prevent them from exploding under charging. All of them.
Typically, those valves will open and blow off excess pressure after extended charging at well less than 15 volts @ 75F or so. The difference with Lifeline has to be not that they have valves--but that their construction allows for higher pressures before the valves blow it off. Or the cases explode.

Other makers swear that AGMs just don't have the ability to have sulphate problems, because there is no liquid electrolyte so no precipitate can form, and any material that does form, is still constrained to the area of the plate.

Somewhere in between the two stories, reality ought to lie. Ergh, lay.
 

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The way I say it Labatt, your issue is either with your charger or the batteries right??? You basically need to eliminate one or the other.

My gut is saying that after 5 years cruising, even with AGM's its probably the batteries. Have they been allowed to drop down around 50% often??
What kind of AGM's are you using, and do you know how many cycles they are rated for? If you do with a quick bit of math based on your cruising you should be able to tell if you get to 5 years or not.

Now one way of proving its not your charger is to of course charge from another source. Shore Power might be the easy answer if access to shore power is a possibility, if not ask around the anchorage for a standalone charger to run off your Generator?. By connecting a different multi-phase charger and running it straight from shorepower/generator to your battery bank, you can eliminating all variables such as connections etc in your system, and tell for sure if it is the batteries or something else.

Best of luck.
 

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Labatt—

How is 12.75 VDC not 100% charged??? This is a 12 VDC system we're talking about, yes??
 

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Discussion Starter · #20 ·
SD - They are AGM's. AGM's are fully charged at somewhere above 12.80v while sealed or flooded lead acid are charged at 12.7v. Gels are actually full at 12.85v+. By the way, my message above should have read 12.65v, not 12.75v. 12.60v on an AGM is about 75% charged. 2 weeks ago I could bring them up to 12.80v with a reasonable amount of time on the genset, and 12.88v on shorepower. All of a sudden, I can barely bring them past 12.65v.
 
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