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Old 02-03-2018, 15:06   #16
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Re: Maintenance Free Batteries

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Originally Posted by john61ct View Post
…There is no gadget that will tell you SoH accurately. You need to have a proper 20-hour load test run, Maine Sail's HowTo site gives a step by step for that.
Thanks John. So there are no load testers worth their $$?

And I’m still curious about the resting voltage of, say a 50% capacity battery. I’m certain my previous bank’s resting voltage was below 12.7 v, which helped me decide to replace them. Resting voltage tells you nothing about battery health?

A 20-hr load test hard to do if you’re living on the boat. But maybe if I isolate each battery, one at a time…
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Old 02-03-2018, 15:14   #17
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Re: Maintenance Free Batteries

Well if a resting battery can’t hold voltage it is probably dead. But it was critical before. My start battery may have been dead for a year before I found out because my house battery feeds the start circuit.

But I bet odds are that a battery at 50% capacity fully charged at rest still has 12.7v or whatever. It is after all fully charged, it just doesn’t have as much capacity. That’s the normal slow dearth of batteries.
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Old 02-03-2018, 19:51   #18
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Re: Maintenance Free Batteries

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Thanks John. So there are no load testers worth their $$?
load testers are good for testing starting batteries. because all you care about is CCA. and holding voltage under big load.

for deep clycle, low load testing. you need to test low load for long time. IE c20 test.
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Old 02-03-2018, 21:12   #19
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Re: Maintenance Free Batteries

Similar question gets into testing by Maine Sail.

https://forums.sailboatowners.com/in...teries.190209/
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Old 02-03-2018, 22:10   #20
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Re: Maintenance Free Batteries

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Similar question gets into testing by Maine Sail.

https://forums.sailboatowners.com/in...teries.190209/
Thanks Stu, and Mainsail, and everyone else. I get it (finally).

OK, hands up. Who here has done a proper 20-hr capacity test of their active cruising battery bank?
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Old 03-03-2018, 04:35   #21
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Re: Maintenance Free Batteries

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OK, hands up. Who here has done a proper 20-hr capacity test of their active cruising battery bank?
You seriously think some cruiser is going to do that? Closest I get is to compare the voltage reading, AH out, and the SOC readings on my battery monitor and see if they all make sense as a group. Of course then I also have to decide what the voltage would be if I turned everything off and waited for the batteries to rest (which I'm not going to do).

If under your normal use the voltage doesn't get low you have enough capacity. As I say, let's stop obsessing about these stupid boxes of lead and acid. They are here to serve us, we aren't here to serve them.
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Old 03-03-2018, 04:41   #22
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Re: Maintenance Free Batteries

Well, the sure fire auto mechanic way to test batteries is to load test with a “carbon pile” tester - available at certain cheap hardware stores in the US. Can’t mention their name but it rhymes with Farber Straight. Last I saw a suitable load tester there was less than $50 US.
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Old 03-03-2018, 04:59   #23
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Re: Maintenance Free Batteries

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Well, the sure fire auto mechanic way to test batteries is to load test with a “carbon pile” tester - available at certain cheap hardware stores in the US. Can’t mention their name but it rhymes with Farber Straight. Last I saw a suitable load tester there was less than $50 US.
Auto mechanics don't deal much with deep cycle house batteries

Carbon pile testers are fine for testing a starter battery or a car battery's "cranking amps" but they are of little value in determining the capacity of a deep cycle house battery.
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Old 03-03-2018, 05:52   #24
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Re: Maintenance Free Batteries

The automated testers that do work cost thousands, specialized engineering lab equipment.

Most owners have a pro do the 20-hour load testing, MS howto spells it out but I would only try it on shore power.
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Old 03-03-2018, 05:54   #25
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Re: Maintenance Free Batteries

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And I’m still curious about the resting voltage of, say a 50% capacity battery
Remember capacity should mean SoH not SoC, so nothing to do with voltage.
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Old 03-03-2018, 09:53   #26
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Re: Maintenance Free Batteries

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Remember capacity should mean SoH not SoC, so nothing to do with voltage.
Yes, thanks John and co. I’m slow … but I think I’ve got it now .

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You seriously think some cruiser is going to do that? Closest I get is to compare the voltage reading, AH out, and the SOC readings on my battery monitor and see if they all make sense as a group. Of course then I also have to decide what the voltage would be if I turned everything off and waited for the batteries to rest (which I'm not going to do).

If under your normal use the voltage doesn't get low you have enough capacity. As I say, let's stop obsessing about these stupid boxes of lead and acid. They are here to serve us, we aren't here to serve them.
That’s my point … and I agree. After now (finally) understanding all this stuff I’ve come to the same conclusion. Almost no normal real life cruiser is going to ever undertake a proper capacity test. And as MS painstakingly points out, if you don’t do it properly, it’s probably not worth doing.

I’m fully with you Don; monitor voltage readings under load, keep tract of AH and SOC. Being aware of any negative trends in performance over time is probably the only viable way for cruisers to realistically monitor battery health.

If it comes to the point where you think you should conduct a full 20-hr capacity test b/c you wonder if your batteries are toast, then much like reefing, if you are asking the question then the answer is probably YES.
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Old 04-03-2018, 19:02   #27
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Re: Maintenance Free Batteries

Thanks team for all the info.
I'll try and do the battery test ex sailboatowners forum as my yacht is currently on the hard and I can use shore power while the batteries are being tested.
Pretty sure my alarm goes off at 11.8v now I think about it.
I'll going across atlantic & pacific so want to be sure batteries are up to it.
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