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Old 15-02-2009, 08:56   #1
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Battery Charging Issue

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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Old 15-02-2009, 10:32   #2
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Before getting to involved in the minutia, I'd verify that every single connection throughout the electrical system including the batteries are clean and tight. After doing that, have the batteries load tested before going on to the charger. In other words, start with the simple stuff.

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Old 15-02-2009, 12:39   #3
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Definitely agree w/ Illusion's advice...

Had a very similar issue with mine, it ended up being caused by the battery voltage sensor circuitry: Fairly thin gauge wires (~16) with inline fuse... It turned out I somehow cracked the fuse housing and it was making intermittent connection, driving the charger nuts.

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Old 16-02-2009, 10:52   #4
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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. 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.
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Old 16-02-2009, 13:58   #5
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recently had similar problems. used a hydrometer in the end and found 2 batteries had faulty cell. Removed these 2 from circuit and working better than it had for years
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Old 20-02-2009, 22:16   #6
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Barring bad/broken instrumentation wiring, I suspect that your battery bank is nearing its end of life. Take a look at the Charge Efficiency Factor (CEF) on the Link. If it is below 80%; the bank is near the end of its life.

As a second check, find a marine electrician with a Midtronics electronic battery conductance tester to test each battery individually. It works by inputting the battery's listed amp-hr rating, performing a ten second test, and having the Midtronics tester read out the actual amp-hrs available.
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Old 22-02-2009, 15:19   #7
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Chris, have you checked the voltage supplied at the battery charger when reading 12.75v on the monitor ?

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