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  1. #1
    Big Traveler Grandesigner's Avatar
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    AGM battery health

    So my 2 size 31 AGMs are coming up on their 18 month free replacement warranty and I thought I would 'test' them by disconnecting the solar system while not on shore power. I wasn't thrilled with their performance last fall and wasn't sure how good they were.
    For the last 3 days they have remained at 12.5 V, which shows they are stable but they get charged at close to 14 V by the solar.
    Is this good or bad?
    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

  2. #2
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    It would depend on what load. AGMs typically have OCV of 12.8 to 13.2V. But to see that you need to disconnect them from everything.
    John & Kathy
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  3. #3
    Big Traveler Grandesigner's Avatar
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    Thanks. I have nothing powered on, so only parasitic loads like smoke sensors and such are drawing very small power.
    Down to 12.4 this morning...
    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

  4. #4
    Long Hauler
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    The CO detector will also likely be on. As was said, you need to completely disconnect the battery/ies form load. Otherwise it's not a valid "test". Have you physically checked the parasitic draw when they're supposed to be disconnected? Load testing is a good way to check the condition of the battery/ies.
    Howard and Peggy
    2019 Momentum 351M, and 2018 RAM Cummins dually 6-speed.
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    Site Team traveldawg's Avatar
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    I would think you need a load tester to check a battery's health.

    A steady state voltage might tell you that all the cells are OK but that's about it I suppose. I'd want to know what happens when a load is applied and how long I can run on the batteries.
    Larry KE4DMG
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  6. #6
    Big Traveler Grandesigner's Avatar
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    I don't have a load tester and was just wondering if it would be worth it to remove the batteries and have them tested where I bought them. They are a literal pain to R&R...
    When I disconnected the solar, the voltage dropped quickly from 13.8 to 12.9 and by the next morning were at 12.5
    The solar app shows 12.3 as the min lately.
    Do local car parts stores 'rent' a load tester?
    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

  7. #7
    Long Hauler
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    It's possible that O'Reilly's would have one to loan, but couldn't swear to it. Have you actually, physically checked the drain on the batteries when they are disconnected from the solar/shore power? If you have a bit of a draw, that would explain why the batteries look like they're failing, when the voltage keeps dropping.
    Howard and Peggy
    2019 Momentum 351M, and 2018 RAM Cummins dually 6-speed.
    His: 1999 Honda Interceptor
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  8. #8
    Big Traveler Grandesigner's Avatar
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    Not sure I can check the drain with my basic multi-tester. I will look into borrowing a load tester before removing those beasts from the awkward location.
    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

  9. #9
    Long Hauler
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    What I'm thinking is you may have parasitic loads that are slowly draining the batteries when they aren't hooked up to solar or shore power. The batteries could be okay, but not look like it because they seem to be losing charge when they're not actively being charged. But they may be losing charge due to parasitic loads. That's what you need to determine before almost anything else. A clamp-on ampmeter is what I use to determine if the batteries are subject to loads when they should be completely idle.
    Howard and Peggy
    2019 Momentum 351M, and 2018 RAM Cummins dually 6-speed.
    His: 1999 Honda Interceptor
    Hers: 2013 Spyder ST-S

  10. #10
    Big Traveler Grandesigner's Avatar
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    I'm sure there are the usual parasites like the propane and maybe CO detectors.
    I only pulled the solar fuse to see what the batteries would do, like on Monday.
    The reason being that I had to use the truck (as a generator) in the mornings a few times when the voltage would hit 12 or lower on our last trip out, even though they would be at 100% before sundown. Yeah the furnace would run at night, but not a whole bunch.
    I am probably going to get an inverter generator this winter for when solar does not cut it, but I still want to know if the batteries are good or not before I go thru the hassle of taking them back before warranty runs out.
    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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