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Old 07-04-2018, 05:30   #1
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Verifying that a battery needs replaced with a hydrometer

I am about to replace my house batteries. Tried to find a thread in the forum, I am sure there is one but was unsuccessful.

What is the way to test a battery using a hydrometer? I believe you charge the batteries to 100%. Test to verify with the hydrometer, disconnect, let stand then retest.

If this is true, how long do you let them stand disconnected from the circuit and each other?

I suspect it would be wise to test each cell at the beginning also when disconnected from the system and each other then after a period retest and compare the results.

Thanks, Aloisius
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Old 07-04-2018, 10:27   #2
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Re: Verifying that a battery needs replaced with a hydrometer

A hydrometer will tell you State of Charge, but not State of Health, except, in very general terms comparing precisely calibrated readings over time compared to benchmarks established when near new, looking at changes over long time periods.

A 20-hour load test is the only reliable way to determine residual capacity, at least without lab gear costing thousands,

and a bank should be replaced when that falls to 70-75% of rating when new, industry standard is 80%.

Most people just keep using until performance is noticeably impaired, take twice as long to get back to 100% Full.

But that leaves you open to "sudden unexpected failure", best avoided.

Others just replace on a schedule, say every five years.

If you want details on doing a 20-hour load test, Maine Sail's site has that, in one of the BM articles.
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Old 07-04-2018, 16:08   #3
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Re: Verifying that a battery needs replaced with a hydrometer

You might spend some time with Battery Maintenance | Trojan Battery Company
. While the information is for Trojan batteries it generally applies to all flooded lead acid batteries.
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Old 07-04-2018, 18:00   #4
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Re: Verifying that a battery needs replaced with a hydrometer

On this day, I would go with a refractrometer instead of a hydrometer. Easier to use and good for antifreeze as well.

But it only tells SOC.
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Old 07-04-2018, 18:52   #5
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Re: Verifying that a battery needs replaced with a hydrometer

After topping up the battery with water and a thorough charging, the six cells in a 12V flooded lead acid battery should all have about the same hydrometer reading. If a cell is 0.050 lower than the others and remains so after an equalization charge, that cell is "dead", and it is time (and maybe past time) to consider replacing the battery.

Note that Trojan (in the link above) begins to worry when the cell to cell difference in a battery exceeds a much tighter 0.007, but I find it hard to be that accurate even with a good glass hydrometer with a float and thermometer.

You can also later re-check the battery after it has been discharged to find a cell that has a lower capacity than the other cells in the battery. The low capacity cell will have the biggest change in its specific gravity.
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Old 09-04-2018, 06:04   #6
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Re: Verifying that a battery needs replaced with a hydrometer

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Originally Posted by wsmurdoch View Post
After topping up the battery with water and a thorough charging, the six cells in a 12V flooded lead acid battery should all have about the same hydrometer reading. If a cell is 0.050 lower than the others and remains so after an equalization charge, that cell is "dead", and it is time (and maybe past time) to consider replacing the battery.

Note that Trojan (in the link above) begins to worry when the cell to cell difference in a battery exceeds a much tighter 0.007, but I find it hard to be that accurate even with a good glass hydrometer with a float and thermometer.

You can also later re-check the battery after it has been discharged to find a cell that has a lower capacity than the other cells in the battery. The low capacity cell will have the biggest change in its specific gravity.
FINALLY! Someone that just answers the OP's question. Well done.

I half expected someone would post about about batteries made from potatoes before the answer might finally show up.
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Old 09-04-2018, 06:41   #7
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Re: Verifying that a battery needs replaced with a hydrometer

Thanks all. I have printed the Trojan Battery article and will keep it in my files. Great article. Will next equalize the batteries again and follow the articles recommendation, although I believe it is to late and will need to replace. The batteries are at least 5 years old.

Where I have my mooring I have plenty of wind and constant sun, I'm in the Caribbean. My trip over Easter I anchored in a couple of spots that had the sun but not the wind. My batteries kept going VERY low. I have the engine batteries isolated from the house so was able to always start the engine.

Aloisius
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Old 09-04-2018, 07:07   #8
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Re: Verifying that a battery needs replaced with a hydrometer

Quote:
Originally Posted by landonshaw View Post
I am about to replace my house batteries. Tried to find a thread in the forum, I am sure there is one but was unsuccessful.

What is the way to test a battery using a hydrometer? I believe you charge the batteries to 100%. Test to verify with the hydrometer, disconnect, let stand then retest.

If this is true, how long do you let them stand disconnected from the circuit and each other?

I suspect it would be wise to test each cell at the beginning also when disconnected from the system and each other then after a period retest and compare the results.

Thanks, Aloisius
We purchased one of these off of Amazon, the high end model, was $100....have found it to be a great tool

https://www.bing.com/images/search?q...ster&FORM=IGRE
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Old 09-04-2018, 07:22   #9
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Re: Verifying that a battery needs replaced with a hydrometer

Nice tester. For $100US it seems to be an efficient tool. Thanks
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