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  1. #11
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    What is your determination if the batteries are good or not? With parasitic drain, they are going to go below whatever voltage they were before you unplugged the solar/shore power. What's your criteria for being bad? Just curious.
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  2. #12
    Site Sponsor sande005's Avatar
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    Battery University has a lot of info about testing. Here's one link: https://batteryuniversity.com/articl...asure-capacity
    Much more on that site about how to test, what voltages "should" be at what level of charge, etc.

    A load test at an auto place will not give much of an indication of "how long it will last", as it is intended to estimate a CCA surge for starting a car. Better is to put a known load on it, and chart the voltage drop over time (although they note that this is not a "hard" number either...)

    Note that a battery should be rested for 24 hrs after coming off a charger, before measuring it's "full" voltage and doing a discharge test. The drop you're seeing can be pretty normal, as it needs time to get into equilibrium.
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  3. #13
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    Quote Originally Posted by Hoopy Frood View Post
    What is your determination if the batteries are good or not? With parasitic drain, they are going to go below whatever voltage they were before you unplugged the solar/shore power. What's your criteria for being bad? Just curious.
    Testing is not possible if there is any load on the battery. After completion of charging, if you turn the charger off the battery will hold a surface charge and remain close to the charger voltage for several hours. Over 6 or 8 hours, the voltage will drop until it reaches that particular battery’s designed 100% charge open circuit voltage at a particular temperature. A good battery should hold at the full charge OCV for days or weeks. Conventional lead-acid 12V batteries at 25 degrees C have full charge voltages of 12.65 to 12.72V. Trojan batteries are the only ones I know of at 12.72V. AGMs have full charge voltages from 12.8-13.2V. Optimas are the high voltage case. Most are 12.8-12.84V. 0.01V is significant.

    You need to find your battery’s OCV, charge the battery, disconnect everything, then measure OCV after sitting overnight. Anything less than the rated OCV indicates a problem, with a bigger difference indicating a bigger problem.
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  4. #14
    Big Traveler Grandesigner's Avatar
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    Quote Originally Posted by Hoopy Frood View Post
    What is your determination if the batteries are good or not? With parasitic drain, they are going to go below whatever voltage they were before you unplugged the solar/shore power. What's your criteria for being bad? Just curious.
    There is no determination yet, only a question; What's the criteria for being bad?
    Same question since post #1 , really.
    Dan and Rita
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  5. #15
    Big Traveler Grandesigner's Avatar
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    Thanks John and Sande05, for getting me out of an endless loop, lol
    BTW, mine dropped almost 1 V within minutes, but yeah, with parasitic load. I can do it over and remove all load potential and/or borrow a load tester...
    Last edited by Grandesigner; 01-14-2022 at 03:18 PM.
    Dan and Rita
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  6. #16
    Big Traveler Grandesigner's Avatar
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    Quote Originally Posted by jkwilson View Post
    Testing is not possible if there is any load on the battery. After completion of charging, if you turn the charger off the battery will hold a surface charge and remain close to the charger voltage for several hours. Over 6 or 8 hours, the voltage will drop until it reaches that particular battery’s designed 100% charge open circuit voltage at a particular temperature. A good battery should hold at the full charge OCV for days or weeks. Conventional lead-acid 12V batteries at 25 degrees C have full charge voltages of 12.65 to 12.72V. Trojan batteries are the only ones I know of at 12.72V. AGMs have full charge voltages from 12.8-13.2V. Optimas are the high voltage case. Most are 12.8-12.84V. 0.01V is significant.

    You need to find your battery’s OCV, charge the battery, disconnect everything, then measure OCV after sitting overnight. Anything less than the rated OCV indicates a problem, with a bigger difference indicating a bigger problem.
    Well I can't find the OCV for my Duracell 31dtmagm batteries but here are some readings;

    Date
    Voltage, time, temp *F

    Jan 15
    14.1 at 11a fully charged, then no solar
    13.2 at 1110a then unhooked from 5W
    12.91 at 1p
    12.86, 5p, 45*

    Jan 16
    12.81, 1030a, 44*
    12.81, 5p, 57*

    Jan 17
    12.78, 1030a, 41*
    12.78, 5p, 55*

    Jan 18
    12.76, 1020a, 46*
    12.78, 530p, 56*

    Jan 19
    12.76, 10a, 50*
    12.77, 5p, 53*

    Jan 20
    12.74, 10a, 42*

    From what I gather from the net, these batteries are made by East Penn, but I can't find specs for them.
    Last edited by Grandesigner; 01-20-2022 at 02:07 PM.
    Dan and Rita
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  7. #17
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    Quote Originally Posted by Grandesigner View Post
    Well I can't find the OCV for my Duracell 31dtmagm batteries but here are some readings;

    Date
    Voltage, time, temp *F

    Jan 15
    14.1 at 11a fully charged, then no solar
    13.2 at 1110a then unhooked from 5W
    12.91 at 1p
    12.86, 5p, 45*

    Jan 16
    12.81, 1030a, 44*
    12.81, 5p, 57*

    Jan 17
    12.78, 1030a, 41*
    12.78, 5p, 55*

    Jan 18
    12.76, 1020a, 46*
    12.78, 530p, 56*

    Jan 19
    12.76, 10a, 50*
    12.77, 5p, 53*

    Jan 20
    12.74, 10a, 42*

    From what I gather from the net, these batteries are made by East Penn, but I can't find specs for them.
    East Penn AGMs are typically 12.8V at 70F 100% charge. You’ll usually see about 0.009V drop for 10 degrees colder, so at 40-ish I’d expect you to be about 0.025V low or 12.775V. You aren’t far off, and without specific numbers from East Penn I’d assume it’s okay.
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  8. #18
    Big Traveler Grandesigner's Avatar
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    Thanks John,
    I was thinking of doing a load test also with this handheld tester I borrowed.
    Attached Thumbnails Attached Thumbnails 20220120_143433.jpg   20220120_143408.jpg  
    Dan and Rita
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  9. #19
    Site Team traveldawg's Avatar
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    I used one of those on the AGMs I just removed from my RV. After sitting uncharged for a few days I got a medium good reading before applying the 'load'. When I switched on the load the needle fell to the weak zone (near to the good reading but definitely in the weak zone).

    I'll be testing them next week with a professional tester borrowed from a friend. I'll try to report the results.

    My batteries have a 3/18 manufacture date.
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  10. #20
    Big Traveler Grandesigner's Avatar
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    I should also mention that it gets down to the teens and 20s here at night with no effort to keep the batteries warm...
    Dan and Rita
    2021 Reflection150 260RD, built June 2020, w/400W solar + 2 size 31 AGMs, added 2" lift blocks to match the
    2022 F350 SCSB 7.3 GdZa 4x4, 10 Sp w/4.30s - Lariat Sport in Atlas Blue

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