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Determining health of AGM battery

bern64
bern64 Member Posts: 6
in Battery/Electrical & Solar

2020 T@B400 Boondock Lite (Solar), purchased Sept 2023

Harris Battery, AGM, 2 x 6V batteries 

I just returned from a trip to Colorado and Utah where on 3 occasions I boondocked at National Parks for 1 night.  The only measure of battery strength I had, was the panel display(yes, I know it is not reliable). Within 1 hour of setting up camp, the display indicated battery was low.  Also, when I tried to use propane setting on the Alde for heat, a low battery warning alert displayed.  

Today, at home I turned off the battery switch and used a multimeter to test battery.  Everything was turned off in the camper.  The reading I got was 13.7, which I know is NOT accurate.  How do I get an accurate battery health reading?  Do I have to disconnect the converter/charger? If so, how?


Bernadette / 2020 (8/2019) T@B 400 BD / 2023 Honda Ridgeline / St. Louis region

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Comments

  • Sharon_is_SAM
    Sharon_is_SAM Member Posts: 10,061
    Use the Victron App to disable the solar charging, turn off the battery switch, make sure the inverter is off.  This should isolate the battery and allow a resting measurement.  
    Sharon / 2017 T@B CSS / 2015 Toyota Sienna Minivan / Westlake, Ohio
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  • AnOldUR
    AnOldUR Member Posts: 1,725
    edited November 2024
    B)
    Stockton, New Jersey
    2020 nuCamp T@B 320S * Jeep Wrangler
    60,865 camping miles through the end of 2025

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  • rfuss928
    rfuss928 Member Posts: 1,180
    edited October 2024
    Measuring resting voltage will only tell the state of charge.  It is not an indicator of capacity.  An aging battery may still charge and discharge normally just with a lower capacity than when new.
    To determine capacity the battery needs to be fully charged then a known load applied and timed while state of charge is monitored.  Generally best accomplished on an analyzer at a battery shop.
    Depending on use and care, 4 to 6 years is common life expectancy of AGM batteries.  The OP batteries fall in this range.
    AnOldUR  - AGM batteries do not require venting. 

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  • Grumpy_G
    Grumpy_G Member Posts: 710
    @AnOldUR if you look to the right side of the batteries there is a hole in the bottom that vents to the outside. AGM batteries do not need venting in normal operation but they can gas off when something goes haywire with the charging voltage.
    As @rfuss928 stated the only good way is to determine the health of batteries is a proper capacity test. You already have a voltmeter, if you have a way to measure current you can calculate capacity from current x time to discharge from full to 11.5 V with a 5-10A load.
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  • bern64
    bern64 Member Posts: 6
    Sharon_is_SAM said:
    Use the Victron App to disable the solar charging, turn off the battery switch, make sure the inverter is off.  This should isolate the battery and allow a resting measurement.  
    Thank you, Sharon_is_SAM.  I disabled solar charging with the Victron App, the battery switch is off, and ensured the AIMS power switch is OFF on the panel by the door.  I took a reading right after and got 13.6.  Then 1/2 hour later got 13.2, and 1 hour later got 12.8.  How long should I have to wait to get a reliable resting reading? 

    Everyone - thanks for the feedback.  I have no problem replacing the batteries, if necessary.  What is the purpose of the chart below that I copied from a post on this forum?  I thought this chart showed battery health.  

    Bernadette / 2020 (8/2019) T@B 400 BD / 2023 Honda Ridgeline / St. Louis region

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  • AnOldUR
    AnOldUR Member Posts: 1,725
    edited November 2024
    B)
    Stockton, New Jersey
    2020 nuCamp T@B 320S * Jeep Wrangler
    60,865 camping miles through the end of 2025

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  • Sharon_is_SAM
    Sharon_is_SAM Member Posts: 10,061
    @bern64 - you are supposed to wait 24 hours before getting a rested battery voltage reading, but, for most, waiting a 1-3 hours will come close enough.   The chart provides the amount of available energy in the battery as a percentage of a rested battery.  But, voltage alone is not the best way to monitor the status of a battery as a load applied will drop the voltage temporarily and a charge will temporarily raise the voltage.   A shunt factors in multiple variables like voltage, age, efficiency, current etc to give a more reliable indication of state of charge.  

    We too have an aging battery.  We have a Victron shunt and we adjusted (reduced) our efficiency and capacity to have the shunt reflect a more accurate state of charge.  When our battery was healthier, we could charge it fully and it would still be close to 100% after 6 months.  Now, we charge it fully and the charged voltage settles down to 12.6 to 12.7 and drops to 12.4 after a couple months.  The aging battery can’t hold a charge as long and discharges sooner.  BTW, there are a lot of charts out there that do not define charging vs rested voltage.  See below.

    Voltage

    Capacity 

    13.00V

    100% (charging)

    12.85V

    100% (resting)

    12.80V

    99%

    12.75V

    90%

    12.50V

    80%

    12.30V

    70%

    12.15V

    60%

    12.05V

    50%

    11.95V

    40%

    11.81V

    30%

    11.66V

    20%



    Sharon / 2017 T@B CSS / 2015 Toyota Sienna Minivan / Westlake, Ohio
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  • Grumpy_G
    Grumpy_G Member Posts: 710
    bern64 said:
    Thank you, Sharon_is_SAM.  I disabled solar charging with the Victron App, the battery switch is off, and ensured the AIMS power switch is OFF on the panel by the door.  I took a reading right after and got 13.6.  Then 1/2 hour later got 13.2, and 1 hour later got 12.8.  How long should I have to wait to get a reliable resting reading? 

    Everyone - thanks for the feedback.  I have no problem replacing the batteries, if necessary.  What is the purpose of the chart below that I copied from a post on this forum?  I thought this chart showed battery health.  

    Lead acid batteries have a "surface charge" effect where they read higher than their nominal voltage right after the charger is disconnected. It depends on the battery but after 2hrs it should read fairly accurate.
    The chart shows the state of charge (SOC) vs measured voltage, it does not indicate battery health. It's not a very useful chart in my opinion because different batteries behave differently. I have some old batteries sitting around that "recover" to over 12V after dropping below 10V under load. 

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  • pthomas745
    pthomas745 Administrator, Moderator Posts: 4,527
    You can get a "rested" readout in just a few minutes that will help you considerably, especially if  you are out camping.  A few hours may be good sitting in your back yard, but out in the cold and dark, go with a short time period.  Not many of us have meters that will actually show 5 digits of voltage.

    The "state of charge" charts that are very common around the web don't vary much.  That 13.0 number is a bit of an outlier.  Voltage for a lead acid battery is more of a "very good estimate" rather than something you can take to the bank.
    2017 Outback
    Towed by 2014 Touareg TDi
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  • bern64
    bern64 Member Posts: 6
    I think I confirmed with many multimeter tests over the weekend that my battery is toast.  The rested readout is about 11.09.  Can you look over my chart and confirm?  


    Bernadette / 2020 (8/2019) T@B 400 BD / 2023 Honda Ridgeline / St. Louis region

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  • manyman297
    manyman297 Member Posts: 1,433
    Our AGMs went out this spring. The main symptom was a huge and fast drop in voltage and then once the solar panel got just the smallest amount of sun the voltage shot right back up. Extremely weird behavior. If you have a Victron smart shunt you can clearly see this behavior in the graph/history.
    2021 400 BD
    2020 Tacoma TRD Off-Road 
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  • pthomas745
    pthomas745 Administrator, Moderator Posts: 4,527
    @bern64 I salute your great testing process and the spreadsheet!
    And, I would agree with your assessment.  The battery is not holding a charge.  The only positive readings you are getting is from voltage going into the battery from either the solar or the shore power connection. The only time it seemed to hold a charge was on that first day.  After that, even after anywhere from 5 to more than 12 hours of charging, the battery kept returning to that very low voltage.
    The Harris batteries just seem to be failing in a wave over the last year or so, after only 3-4 years of use.
    There are many threads about replacing the dual 6V with a single 230 amp hour lithium battery that will increase your usable amp hours to around 200 compared to the dual 6V's 135 or so.
    This thread discusses a lithium replacement, along with the possibility of replacing your current battery setup with equivalent 6V AGM's, which are still available if you want to stay with them.

    2017 Outback
    Towed by 2014 Touareg TDi
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  • Trailpixie
    Trailpixie Member Posts: 191
    A side note on AGMs--some have a standard resting voltage of 12.8 volts. This doesn't affect its capacity. Check the spec of your battery to see what its resting voltage should be.
    T@B 360 Black Canyon, 2021 Jeep Grand Cherokee V6, Maryland
    (previous 2018, T@B 320 Outback)
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  • Cherokee
    Cherokee Member Posts: 346
    The best way to prolong the life of your batteries is to keep them on a trickle charger that keeps them fully charged when the trailer is stored
    TV:2019 Nissan Frontier PRO-4X With an Old Man Emu lift
    Trailer: 2019 T@B 320 Boondock with a Lock&Roll Coupler & Jack-e-up
    Custom fabricated metal bottom cladding
    California, USA
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  • Cracker
    Cracker Member Posts: 30
    Cherokee said:
    The best way to prolong the life of your batteries is to keep them on a trickle charger that keeps them fully charged when the trailer is stored
    Won't the solar panel maintain the charge?
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  • Cherokee
    Cherokee Member Posts: 346
    Cracker said:
    Cherokee said:
    The best way to prolong the life of your batteries is to keep them on a trickle charger that keeps them fully charged when the trailer is stored
    Won't the solar panel maintain the charge?

    maybe in sunny south California - here in NoCal, we have a rainy season that last for days on end when the panels would not produce much electrical energy. Obviously,  those in the rain forest in Washington state can't ether 
    TV:2019 Nissan Frontier PRO-4X With an Old Man Emu lift
    Trailer: 2019 T@B 320 Boondock with a Lock&Roll Coupler & Jack-e-up
    Custom fabricated metal bottom cladding
    California, USA
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