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Beware - The Battery Monitor Indicator Lights May Not Indicate the Battery Level

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  • Beware - The Battery Monitor Indicator Lights May Not Indicate the Battery Level

    Applies to 2020 3740BH-R (...or a least the one I own LOL)

    Greetings Everyone,

    I just discovered the battery level monitor lights that you activate by pressing the battery button at the Convenience Center does not indicate the battery level on our beloved 3740BH-R when shore power is on. It is attached to the Converter side of the battery switch and indicates the voltage output of the 110V to 12 V converter when the rig is plugged in.

    I discovered this while installing a bank of 4 Interstate SRM-24 batteries and had all batteries unattached (and shore power was on). I went inside to check my tank levels and decided to press the Battery button for grins and all four lights lit up indicating a full charge. What??

    Now I remember the first move I made, I went to pick up the levelers and the leveler control panel wouldn't come on. I checked the battery voltage with a meter and it was less than 10 volts because the battery switch had been shut off and the batteries will not charge with the switch off. When I discovered the low voltage I went in and pressed the Battery level indicator and it was 4 lights showing a full charge. I just assumed it was inaccurate.

    I looked in the manual and it states the button is to determine the auxiliary battery level. The secret is you have to shut off the shore power to have an accurate battery reading and not be reading the output of the converter.

    Besides, a good volt meter should be in the kit anyway, right.

    Just something to keep in mind....

    Sarasota Ron

    2020 3740BH-R 2021 Ram 3500



    2020 3740BH-R
    2021 Ram 3500, Cummins, CC, 8' bed

  • #2
    Ron R Ron, even a good multi meter in your kit will not provide an accurate reading on the batteries when on shore power. Remember when on shore power with converter powered, the batteries are receiving charge voltage from the converter. This voltage is higher than the actual charge state of 13.2 for flooded batteries.
    Joseph
    Tow
    Vehicle: 2024 GMC K3500 Denali Ultimate Diesel
    Coach: 303RLS Delivered March 5, 2021
    South of Houston Texas

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    • #3
      To check the status of a battery or battery bank with a meter.
      1 - Unplug from shore power.
      2 - Turn off 12v items such as lights and fans.
      3 - wait 3-5 minutes before taking your voltage reading with the volt meter.
      4 - Compare your measurement to a state of charge chart such as the one I'm attaching below for a 12v flooded lead/acid battery:

      Click image for larger version

Name:	SOC Lead Acid.JPG
Views:	1026
Size:	58.0 KB
ID:	53122

      Jim and Ginnie
      2024 Solitude 310GK
      GDRV Technical Forum Moderator
      GDRV Rally Support Coordinator

      Comment


      • #4
        TucsonJim I think mine always reads 100% regardless of battery state of charge. Everything above makes complete sense. But, for those of us with upgraded (Lithium) battery banks....is there any modification we can make to the LED display so that it would accurately reflect battery charge level?
        2020 Imagine 2400BH
        2017 Ford F350 Platinum FX4/4x4 SuperCrew 6.7L V8 Diesel 9' Bed SRW, Leveled + Airbags

        Our Mods

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        • #5
          Originally posted by bellis View Post
          TucsonJim I think mine always reads 100% regardless of battery state of charge. Everything above makes complete sense. But, for those of us with upgraded (Lithium) battery banks....is there any modification we can make to the LED display so that it would accurately reflect battery charge level?
          Flooded lead acid and AGM batteries have a very distinct discharge curve which allows for an accurate prediction of their state of charge as shown in the chart above. LiFePO4 batteries maintain their voltage throughout discharge, so state of charge charts will be very inaccurate. The most accurate way to determine the state of charge in a LiFePO4 battery is with a shunt style battery meter such as the Victron BVM712. The constant voltage of LiFePO4 batteries is also why the LED battery meter in the coach is almost always showing full.

          Jim
          Jim and Ginnie
          2024 Solitude 310GK
          GDRV Technical Forum Moderator
          GDRV Rally Support Coordinator

          Comment


          • #6
            Originally posted by TucsonJim View Post

            Flooded lead acid and AGM batteries have a very distinct discharge curve which allows for an accurate prediction of their state of charge as shown in the chart above. LiFePO4 batteries maintain their voltage throughout discharge, so state of charge charts will be very inaccurate. The most accurate way to determine the state of charge in a LiFePO4 battery is with a shunt style battery meter such as the Victron BVM712. The constant voltage of LiFePO4 batteries is also why the LED battery meter in the coach is almost always showing full.

            Jim
            I figured....I am happy to rely on my shunt and victron gear....just was trying to think outside the box to see if factory stuff could be fixed back up.
            2020 Imagine 2400BH
            2017 Ford F350 Platinum FX4/4x4 SuperCrew 6.7L V8 Diesel 9' Bed SRW, Leveled + Airbags

            Our Mods

            Comment


            • #7
              The lights don't tell you much. On my panel, light 1 shows low, light 2 shows 11.2, light 3 shows 11.7, light 4 shows 12.3. So going by their numbers, light 3 would be an almost completely dead battery, and light 4 would show a battery that is 70% charged. The KIB display on our old trailer, Light 1 = low, light 2 = med, light 3 = high, and light 4 = charging. About as accurate as the lights showing tank levels. For flooded or AGM batteries, just get an LED voltage display.
              Click image for larger version

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              Last edited by 315RLTSinPA; 05-13-2021, 04:32 PM.
              2018 Reflection 315RLTS
              2023 F350 Lariat 6.7L/CC/LB/FX4

              Comment


              • #8
                Originally posted by 315RLTSinPA View Post
                ... just get an LED voltage display.
                I'm in agreement--learning to interpret the voltage reading of a display (may be slightly different from camper-to-camper due to wiring losses, etc) is something every RV owner should learn. Seeing the voltage drop during normal slide room extension and retraction will help them identify when something is wrong if the voltage drastically varies from the norm. Same with awning extensions and retractions.

                The bluetooth BMV-712 does this for me (should I care to monitor it), but for most a simple swap of a USB outlet for one with a display is something almost every owner could do easily.
                Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.

                2017 Ford F-350 DRW, '19 315RLTSPlus

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                • #9
                  Originally posted by TucsonJim View Post
                  To check the status of a battery or battery bank with a meter.
                  1 - Unplug from shore power.
                  2 - Turn off 12v items such as lights and fans.
                  3 - wait 3-5 minutes before taking your voltage reading with the volt meter.
                  4 - Compare your measurement to a state of charge chart such as the one I'm attaching below for a 12v flooded lead/acid battery:

                  Click image for larger version

Name:	SOC Lead Acid.JPG
Views:	1026
Size:	58.0 KB
ID:	53122
                  There seems to be a lot of variations in the charts to appraise the dc voltage and the percent of battery discharge. I'm currently doing some experimenting with a new group 27 deep cycle battery and then recharging with my Honda EU2000i in preparation for a stay in a campground with no electric hookup, so this is of real interest to me.

                  I've found charts that show 12.3vdc as being 50% discharged, where the above chart shows about 65%. I've also been measuring SG so maybe this would be a more accurate way to go, but again the published values vary also.

                  It seems to be apparent getting to or below 50% discharge will shorten the flooded cell battery's life.
                  2020 Reflection 273MK
                  2005 Dodge Ram 2500 CTD

                  Comment


                  • #10
                    Originally posted by Lonestar View Post

                    There seems to be a lot of variations in the charts to appraise the dc voltage and the percent of battery discharge. I'm currently doing some experimenting with a new group 27 deep cycle battery and then recharging with my Honda EU2000i in preparation for a stay in a campground with no electric hookup, so this is of real interest to me.

                    I've found charts that show 12.3vdc as being 50% discharged, where the above chart shows about 65%. I've also been measuring SG so maybe this would be a more accurate way to go, but again the published values vary also.

                    It seems to be apparent getting to or below 50% discharge will shorten the flooded cell battery's life.
                    One of the best sources I've found for battery information is batteryuniversity.com. There are articles on what happens to a deep cycle battery if it's discharged too deeply or not charged enough.

                    Jim
                    Jim and Ginnie
                    2024 Solitude 310GK
                    GDRV Technical Forum Moderator
                    GDRV Rally Support Coordinator

                    Comment

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