12v Battery - do it myself?

Discussion in 'Clarity' started by su_A_ve, Nov 3, 2023.

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  1. su_A_ve

    su_A_ve Active Member

    2018 PHEV here and "knock on wood" no issues yet. But 2018 Ody already had to get it replaced as it had started to die.

    Looking at Costco which doesn't do it for you, so if the weather is nice, I can head over with the socket wrench set. But my questions:

    * Do you need to clean the battery cables and/or apply any type of lubricant to the posts?
    * How do you prevent the computer/radio from loosing settings?

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  3. petteyg359

    petteyg359 Well-Known Member

    Connect a trickle charger to posts under the hood so the car is still powered after you remove the battery? As long as it's powered off otherwise, it shouldn't be drawing any appreciable current.
  4. insightman

    insightman Well-Known Member Subscriber

    Before disconnecting your 12-Volt battery, plug one of these 9-Volt battery memory-saver dongles into your car's DC outlet (formerly known as a cigarette-lighter socket).

    OneEV and neal adkins like this.
  5. I recently replaced the 12V battery.
    1) Did not lose radio settings. Do not have any sort of scheduled charging programmed so can’t comment on that. Did not lose odometer data.
    2) Did not clean or lube terminals or posts. They were clean, saw no need to take any additional steps.

    I pulled the old battery, took it to the local dealer and purchased the Honda replacement battery for $130. It has a full 3 year warranty and is then pro-rated for 100 months. I was informed at the parts counter that it is believed to be made by Interstate, same as Costco. Whether or not that’s true, I don’t know. It does offer a superior warranty however.

    The warning lights on the dash went off after a few minutes of driving.
    BrianRC likes this.
  6. petteyg359

    petteyg359 Well-Known Member

    Might be safer to build your own with 8 AAs so you actually have 12v and don't risk overheating the 9v battery. Would suck to set the interior on fire.
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  8. insightman

    insightman Well-Known Member Subscriber

    A lot of companies make a version of this 9-Volt device. If you don't believe they can work because a 9-Volt battery is too wimpy, one of these OBDII connectors will hook up to a big-boy 12-Volt battery:

    I've read that as little as 5 Volts will allow a car radio to retain its station memory (and the clock to retain the time). Hopefully you wouldn't try to start the car with the 9-Volt battery--what else would cause a major drain on the little guy during the few minutes it takes to replace the 12-Volt battery? Eight AAs would supply the full 12 Volts, but why would they be less likely to burst into flames?
  9. FWIW: By the time I removed the battery, drove to the dealer, bought a new battery, returned home and installed the new battery, the car had been without a battery for more than an hour. It did not lose any radio settings.

    Why would anyone spend time or money on a gadget in an effort to maintain a 12V power supply while the battery is out.
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  10. neal adkins

    neal adkins Active Member

    I changed my 12 volt battery over a year ago on my 2018 clarity. I don't remember exact steps but just had to drive the car a few minutes before all warning lights eventually went off. I would inspect the terminals carefully and clean as needed then apply a battery terminal spray to prevent corrosion.
  11. lanb

    lanb Active Member

    Question for those who replaced the battery - Did you all get any warning light in the dashboard before it died ?

    The stealership said that my 12v battery is bad but I have not had any issues yet (knock on wood) and the battery
    reads around 12.8V at rest. I plan to get it checked at Sams soon.
    I am a bit skeptical about the dealer because, they always upsell a bunch of services whenever I go in for an oil change.
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  13. neal adkins

    neal adkins Active Member

    I bought a
    I think the battery has an indicator on it if i remember correctly...
  14. No. In my experience the indicator lights on the dash will illuminate after a loss of 12V power. There is no warning prior to a 12V battery failure.

    FWIW: I replaced it with the Honda battery. It was $130 and offered a superior warranty to any other battery on the market.
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  15. lanb

    lanb Active Member

    Thanks both. The indicator on the battery says it is good. I will get it tested at Sams to be sure.
    I will check on the OEM battery cost as well.

    P.S. - 51R is the 12v battery size for clarity, right ?
    Last edited: Dec 23, 2023
    neal adkins likes this.
  16. Correct. The “R” designates that the Positive post is on the right side of the battery. A Group 51 is the correct “size”, however the post configuration would make for a frustrating installation.
  17. rodeknyt

    rodeknyt Active Member

    The stealerships test batteries for CCA regardless of what vehicle they are in. The 12V battery in the Clarity isn't used for anything other than to power the handful of low voltage circuits in the car. Since there is no engine cranking involved with the 12V battery, the testing the stealership does is pretty much irrelevant for us.
  18. su_A_ve

    su_A_ve Active Member


    Finally made an appointment with Sam’s Club and took it in to get it replaced. But Sam’s won’t touch any hybrid or PHEV as there could be programming to be done when replaced.

    Since mine has been ok for 5.5 years, I guess it didn’t have the issues many did with them dying prematurely and since there’s no cold cranking, it should be in decent shape. I’ll keep checking it and wait until the weather is nicer and replace it at Costco’s parking lot.

    BTW, Sam’s gave me some post pads to use..
  19. lanb

    lanb Active Member

    So, if the 12v isn't used for cold cranking (even when the PHEV battery is down to 2 bars) what were the symptoms that made the other folks switch out their battery or in other words, what should I look out for ?
  20. The HV battery always starts the engine, regardless of its SOC. The 12V battery never starts the engine.

    There are no early warning signs to indicate that the battery is becoming weak. Some owners have replaced the battery after a certain amount of time, as a preventative measure, others have waited until the battery fails.
  21. lanb

    lanb Active Member

    Thanks. Going by your earlier post "indicator lights on the dash will illuminate after a loss of 12V power" is the sign of battery failing.
    I am assuming the actual effects on the car when the 12v fails will be the low voltage items like the usb ports stop working, correct ??
  22. Perhaps we define failure differently. I would consider a loss of 12V power to be a battery failure, since the battery failed to provide power to a system which requires 12 volts in order to function.

    The car will not power up when the 12V battery fails. That is the actual effect. As stated previously, there is no warning prior to a 12V battery failure.
  23. bpratt

    bpratt Active Member

    My 12 volt battery failed at 3 years 1 month old, just outside the warranty. The car started and ran fine the day before and would not start the next day. I tried putting a 6 amp charger on the battery and tried to start it. The car gave me a message to disconnect the external charger before attempting to start it. I next tried putting the car in neutral to push it out of the garage so I could jump it. Putting it in neutral is not possible until the car is started.
    So I put the charger back on the battery and let it charge for a couple of hours. After I removed the charger, the car did start, I took it to Honda to get it checked and was told it had a cell that had failed.
    I now carry a 12 Volt LI battery to use if this happens again.

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