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Battery Voltage Check using Multimeter

RobynERobynE Member Posts: 31
in Battery/Electrical & Solar
Hi,  I have a smart shunt so I'm good,  but im just wondering if there is any way to check voltage with multi meter from the 12 volt outlet (or other option?) since batteries are difficult to get to under the bed. I was thinking I might need to help my friend who doesn't have any vitcron monitoring devices.  Thanks
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    techietabtechietab Member Posts: 159
    edited October 2022
    You can (put + lead on the contact at the back, - lead on the outer metal contact that makes up the 'barrel' inside the plug), but you're going to get voltage readings with a voltage drop due to resistance on wiring between the plug and the battery, so it won't be as accurate as a reading directly from the battery.
    If cost and ease of install is a concern that is keeping your friend from investing in a Smart Shunt, they should have a look at the Victron Smart Battery Sense device. It's about $40 USD, super easy to install, and will give you a fairly accurate reading of the battery charge state. It's not quite as good as the Smart Shunt (and will tell you nothing about current load), but I have both installed very close to my batteries (to get temp readings from the batteries) and the Battery Sense device is usually only off from the Smart Shunt readings by 0.02 volts.
    Northern VA
    2022 T@b 320 S / 2021 Subaru Outback
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    Denny16Denny16 Member Posts: 5,431
    You can also add a SAE port (used for external portable solar panel connections) and put it by or in the rear cargo door and use it to meter the battery.  This way the battery cut off switch can be turned off for an accurate rested battery check with all battery loads eliminated.  
    Cheers 
    2018 TaB400 Custom Boondock,  Jeep Gladiator truck, Northern California Coast.
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    kurtkurt Member Posts: 11
    Hello, I use this device, "Jtron® Dc 12v 10a Male Cigarette Lighter Plug with Power Wiring Cable Car to Take Power Black Power Cord for Inverter", available from Amazon. I connect it to my multimeter using two banana to banana cables for a quicker and easer connection, and it also allows my to watch the voltage drop when I turn something on.  There are digital 12V plug in meters designed to monitor your car battery , but I trust the accuracy of my multimeter.

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    subkronsubkron Member Posts: 149
    You can use a 12V outlet.  Since the 12V outlet has no load (it does not have anything connected except the meter) and the meter is high impedance (>>1Mohm) there is virtually no current flowing hence no voltage drop. You would be within microvolts of the actual battery voltage.
    2022 T@B 400 Boondock
    2015 RAM 1500 Outdoorsman Quad Cab
    South Jersey
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    pthomas745pthomas745 Moderator Posts: 3,678
    edited October 2022
    The problem with the devices that use the 12V plugs is: all those readings with the battery switch on will be false.  All of them will read "too low" or "not the actual" voltage reading.  Or, if the battery is being charged, they read "too high."
    The SAE port for the solar setup goes directly to the battery.  With the battery switch off, the "rested" reading of the battery will provide a more accurate readout of voltage.
    The Victron Smart Sense is a nice device.
    There are other little monitors that do the same basic thing.  Just attach to the battery and go.  (Battery switch still needs to be off for a good readout with these devices.)

    There are also inexpensive shunts, but without bluetooth, getting the readout might be a little more of a chore.


    2017 Outback
    Towed by 2014 Touareg TDi
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    ScottGScottG Administrator Posts: 5,449
    edited October 2022
    I've managed eight seasons--mostly camping 4-8 days at a time without shore power--using only an inexpensive plug-in voltmeter. I agree it doesn't give you a completely accurate reading for the reasons stated by pthomas745, but I've developed a pretty good sense of what is normal battery behavior under different circumstances.
    If you are disinclined to battery whispering, crave a steady flow of accurate information, or routinely to push your batteries to the limit, this might not work for you. However, if your needs are modest, monitoring the battery via a 12V outlet is a cheap and easy method that is a big step up from no monitoring at all. 
    2015 T@B S

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    RobynERobynE Member Posts: 31
    edited October 2022
    Thanks so much for all the detailed reponses! For some reason I wasn't getting notified of the responses, so I'm slow to get back to this threat.  Lots of great info. I will take some time and consider all the options and facts.

    Personally, I need to know everything about my battery at a glance, so I had my dealer install the smart shunt (although he did it wrong and I had to fix it) but my friend doesn't even turn her battery switch off when she gets back from trips (claims no need to because solar keeps the battery fully charged....don't get me started on why this isn't a good idea)  She relies only on the panel at the front door which I know is not helpful at all.  
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