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Old 12-03-2022, 03:15 PM   #1
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Checking Batteries

Can I get a accurate reading checking my house batteries connected parallel with a hydrometer without disconnecting them?
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Old 12-03-2022, 03:20 PM   #2
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Yup.
It only measures the chemistry of each cell in the battery.

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Old 12-03-2022, 04:29 PM   #3
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Best results would be with the batteries at " rest " no charging/dis-charging for at least a couple of hours.
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Old 12-03-2022, 04:47 PM   #4
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if they are low on water, would recommend checking before adding distilled water. After charging I would recheck them again.
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Old 12-03-2022, 04:59 PM   #5
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Wow, haven't seen a discussion of checking the specific gravity of cells of a battery for a while!

Many have moved on the sealed batteries, such as AGM or higher end lithiums.

I have not used my hydrometer is years! Any flooded cell batteries that I currently own are just maintained full, and fully charged to a rested voltage of greater than or equal to 12.6 volts. If I have a concern with performance, I just load test.
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Old 12-03-2022, 08:19 PM   #6
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Agree, to much science using a hydrometer.

Need to compensate for temperature and stuff.
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Old 12-04-2022, 10:22 AM   #7
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SG measurement doesn't require disconnecting anything. There are displacement (floating), and refractive testers. SG can be a useful measurement to check SOC and cell balance but isn't terribly precise. Much like the open circuit voltage test the battery must be idle for 24 hours to get an accurate reading.


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Old 12-04-2022, 11:40 AM   #8
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Back when I had flooded, I used a hydrometer to give me a general reading on state of charge. I treated it much like the dash gauge in a car where it isn't so much about absolute accuracy, but instead more about average levels and trends.

One of my first accessories was adding an inexpensive battery monitor. Sure a whole lot easier to look at a meter, than to access the battery tray and test all those cells. Even still, the hydrometer confirmed what I suspected, that the batteries had seen better days. Even after a careful charge and rest, they'd settle down to around 75-80% soc. There wasn't much difference in cell to cell readings which was good. Not as good as a load test, but between the lower rest reading, and the fact they didn't last as long as they should have on a charge, told me it was time for new batteries before depending on them for boondocking.

With flooded cell batteries, even a a battery monitor can be an approximation unless well calibrated, and you do an occasional, timed 20 amp discharge test to know the true amp hour capacity of your batteries. But, any testing or monitoring device is better than nothing, and hydrometers are pretty cheap so it's a good tool to have.
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