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Old 07-28-2014, 01:35 PM   #1
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Please help verify my battery diagnostics

All:

This past Saturday we took our boat out for a few hours on a short evening cruise with friends. About 3/4ths of the way through the trip, I noticed that my battery light on the gauge panel was lightly lit. I confirmed low battery on the breaker panel with the analog gauge showing ~12.5v. Usually it's up near 14v with the alternator output.

We had been cruising at just above idle (~900RPM) for a couple hours, dragging a salmon lure at 2 kts. We pulled up all the gear, turned off all the extraneous 12v loads (namely refrigerator and radar), brought the RPMs up to 1600 and got home without further incident about 20 minutes later. I thought, though, with that amount of runtime the battery bank would be charged above alarm stage, but it wasn't.

We tied into shore power, and I noted that both banks were taking a charge before we went home. Sunday we went back down to the boat to take a look at things. Charge indicators were showing float stage on both banks. Disconnected shorepower, and turned the engine over (just fine, no problems). But even after an overnight charge, the alarm light was still lit. Analog gauge still showing high 12v readings.

I shut down, and went into the engine room. I grabbed a hydrometer to first test the batteries -- every one of my house batteries were bone dry! I couldn't even get enough water to do a test. Starting battery was good to excellent on all 6 cells, so that's good at least.

So my assumption is that the house bank is toast. Also, I'm concerned about the alternator, but not for any evidence. I did not meter the output while down there yesterday, but will do so soon. So my current plan is to first replace the house bank batteries with 6 new group 24s. Then, meter the output of the alternator, and if that is funky at all, look into replacing that as well.

Does that sound reasonable? Any other diagnostic checks, or items I should look at?

Any other money-saving advice?

I really don't like when people ask for help and then don't give enough information to have people around the world help diagnose, so here's a bullet list of the essentials:
  • House bank: 6 group 24s, approximately 5 years old (no stickers marked, going off notes of PO)
  • Starter bank: Single group 31, approximately 5 years old
  • Charger: 20amp Zantrex True Charge
  • West Marine Battery Charge Monitor
  • Battery Isolator: installed (not 100% sure on wiring or manufacturer)
  • Boat was hauled out in March for new bottom paint and basic engine service - no issues discovered
  • Last couple trips the bow thruster has not worked for more than a couple seconds (shuts off). I assumed there was something fouling it and was going to dive it to check, but....
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Old 07-28-2014, 01:52 PM   #2
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Five years is about done for standard batts. You already know dry batts are not good. Some alternators need high rpm to start charging of not used for a while. You didn't say if voltage went up on trip home.
You can't hurt anything by adding water and trying to charge but why bother?
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Old 07-28-2014, 01:53 PM   #3
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Low voltage will cause thruster to shut down sooner.

Usually only one problem. I would start with the batts
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Old 07-28-2014, 01:54 PM   #4
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So my assumption is that the house bank is toast. Also, I'm concerned about the alternator, but not for any evidence. I did not meter the output while down there yesterday, but will do so soon. So my current plan is to first replace the house bank batteries with 6 new group 24s. Then, meter the output of the alternator, and if that is funky at all, look into replacing that as well.

Does that sound reasonable? Any other diagnostic checks, or items I should look at?
Your assumptions certainly sound good to me. Exact same way that I would begin. As you say, the batteries are almost certainly toast, so replacing them is crucial. Checking alternator output not crucial but wise. Even if those things do not completely solve the problem, they have to be done in any case. IMO.
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Old 07-28-2014, 01:55 PM   #5
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Check batt voltage after overnight. Will probably be low.
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Old 07-28-2014, 02:03 PM   #6
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Based on what you posted, if it were my boat, replace the house bank with 6v golf cart batteries if possible.
Dont know if the old batts can be recovered. I would at least try once.
Not a fan of six 12v batts in parallel. Plenty of discussion on the site archives. Search for "battery" or "golf" or "bank" in the title.
If the thruster was powered from the house bank, the short run time was a tell-tale that the capacity was shrinking.
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Old 07-28-2014, 02:09 PM   #7
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Quote:
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You didn't say if voltage went up on trip home.
Voltage went up from approximately 12.3v to just around 12.5v. Where normally I would expect it to be around 14v at that RPM.

Quote:
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You can't hurt anything by adding water and trying to charge but why bother?
Yeah, that's my thinking too. Other than it saves $500, there's no good reason.
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Old 07-28-2014, 02:10 PM   #8
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If your battery charger has an equalizer function, you may possibly bring the batteries back to decent life. Make sure to disconnect all electronics, etc., before beginning the equalize process, as the charging voltage is high enough to be potentially damaging.
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Old 07-28-2014, 02:11 PM   #9
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Quote:
Originally Posted by High Wire View Post
If the thruster was powered from the house bank, the short run time was a tell-tale that the capacity was shrinking.
I didn't think about it a week ago, but that's why I added that bullet point. Thanks for validating that it could be related, I wasn't sure.
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Old 07-28-2014, 02:15 PM   #10
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If you have a bad cell you might get 12.5v when charging like $&@. That's why I suggest checking after sitting. Batts in parallel will dump all charge into bad batt and overheat. Combine that with charging and boil out results.
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Old 07-28-2014, 02:15 PM   #11
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Yeah, that's my thinking too. Other than it saves $500, there's no good reason.
If they were fairly new batteries, then trying to bring them back to life might be worth trying. But for five-year old batteries it is not something which I would bother with. Look upon the $500 as a fine for not having made periodic checks of the water level. :-)
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Old 07-28-2014, 02:19 PM   #12
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While your changing all the batteries be sure to clean and check every connection all up and down the line.

And then start monitoring your battery water levels monthly.
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Old 07-28-2014, 02:21 PM   #13
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Look upon the $500 as a fine for not having made periodic checks of the water level. :-)
Hah, that was my wife's reaction too. "You mean all you needed to do was suck out a bit of water into this thing and see where the balls float to? And because you didn't, we need new batteries?"

...Yeah. Pretty much.
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Old 07-28-2014, 03:42 PM   #14
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If alt light was dim lit and volts only 12.5, you have an alternator problem. If batts were bad, alt would get real hot and struggle to raise volts, but indicator would NOT come on, dim or not.

Start engine and rev it up to say 1200 and check volts right on back of alt using a DVM.
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Old 07-28-2014, 03:50 PM   #15
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Hah, that was my wife's reaction too. "You mean all you needed to do was suck out a bit of water into this thing and see where the balls float to? And because you didn't, we need new batteries?"

...Yeah. Pretty much.
Yeah, well, it could be worse. She could have figured out that you didn't even need the thing with the balls in it. And that all you really had to do was open the caps and look in to tell the levels.
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Old 07-28-2014, 03:50 PM   #16
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So my assumption is that the house bank is toast. Also, I'm concerned about the alternator, but not for any evidence. I did not meter the output while down there yesterday, but will do so soon. So my current plan is to first replace the house bank batteries with 6 new group 24s. Then, meter the output of the alternator, and if that is funky at all, look into replacing that as well.

Does that sound reasonable? Any other diagnostic checks, or items I should look at?

Any other money-saving advice?


I really don't like when people ask for help and then don't give enough information to have people around the world help diagnose, so here's a bullet list of the essentials:
  • House bank: 6 group 24s, approximately 5 years old (no stickers marked, going off notes of PO)
  • Last couple trips the bow thruster has not worked for more than a couple seconds (shuts off). I assumed there was something fouling it and was going to dive it to check, but....

I think I'd water the current batteries, charge 'em, and see what happens. They might surprise you with a bit more service while you think about it. If not, it will only cost you some distilled water and a little bit of time.

You can greatly! improve your house bank with 6v DEEP CYCLE batteries in series-parallel. The Group 24s you have are all essentially starting batteries, even if the say "dual-purpose." Search threads about 6v deep cycle plate thickness, etc.

If the bow thruster works off the house bank, you'll also probably see much improved performance there, too.

-Chris
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Old 07-28-2014, 04:05 PM   #17
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I went w/ the 6v golf cart batts, recommend it.
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Old 07-28-2014, 04:05 PM   #18
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Tell her that checking the balls and associated equipment more frequently with age may prolong life
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Old 07-28-2014, 04:52 PM   #19
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I'm a big fan of golf cart 6V batteries in place of the group 24 batteries if you can accommodate the footprint and height of the GC batteries. You'll get a much larger capacity house bank of approximately 660 AH. I bought mine at Costco and I think they're running about $85-90 per battery. Of course, with that higher AH capacity comes higher charging requirements from alternator and shore charger. It's a domino effect of purchasing requirements.

When I upgraded, I went from a 30A 3-bank smart charger to a single bank 55A smart charger and a combiner. I could have used a larger one, but my little Honda generator is better suited for 55A. I also upgraded my alternator to 120A Balmar with smart regulator. Tonight I'm swinging on the hook at Angel Island with two ladies onboard, the Admiral and her friend, so we'll be using lots of electricity, water and holding tank capacity!! I have monitors for all 3 to keep track of usage.

Water Miser battery caps help reduce loss of battery water. I have used them for 3-4 years and am pleased. There might be better products out there for more money, but these work well for me. (Pay attention to clearance above the battery when selecting the model.)
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Old 07-28-2014, 07:15 PM   #20
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My guess is " slack (non)maintenance causing slow death". You`d need an heroic equalizer function to get the sulfur off the plates back into fresh water.Plus whatever else happened structurally while the batteries gradually dried out and strong charging went in. I`d probably try watering them out of sheer curiosity, if nothing else. Replace with sealed versions?
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