Battery Charger Charges 12v Battery Quickly

Discussion in 'Gen 3 Prius Main Forum' started by Finite Resources, Mar 25, 2022.

  1. Finite Resources

    Finite Resources New Member

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    My prius failed to start one cold morning couple weeks ago. No lights, ac, radio were left on. The only weird thing was I didn't lock the car and hadn't driven maybe a week or so. I had to get a jump and I took it to three different auto stores for battery testing.

    They all said that the 12v battery looks okay. One person said it showed 125 or 325 CCA (sorry, my memory is fuzzy). One person said it was at half capacity but doesn't look like I need to replace it. And the other said the battery looks good and doesn't need to be changed, just charge it.

    The battery is a Toyota Truestart last replaced on 11/2016. Ever since the jump, my car has been working okay. I drive very little (maybe 20-30 mins max for the whole week). After trawling through the forums I learnt about 12v batteries, smart chargers, trickle chargers etc and the need to maintain your battery by charging if you don't drive often. So I ended up buying a cheap $35 4amp smart charger that works on AGM batteries.

    The first time I connected the charger through the front jump points, the charger display showed 12.4v and then as it charged, the voltage went up slowly. But within couple hours, the charger said 'FUL' with full bars. From what I read in these forums, I thought if the battery is old or not charged fully, it will take 8 hours or longer with 4 amp chargers? I waited a day and connected the charger again this morning and it went to FUL charge withing 20 minutes or so, but I just left the charger on for the whole day since it's an automatic smart charger.

    What does this charging time tell you about my battery state? Start looking for a new battery? Since truestart has a 84 month warranty I should be able to get 25% off a new battery if I got to a dealer but I'm afraid all their tests are going to show that my battery is okay.

    Also, is connecting the charger to the battery and checking the charger display for the voltage a good approximate substitution for a multimeter or MFD voltage check?

    Thank you!
     
  2. JC91006

    JC91006 Senior Member

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    I want to first say that tire warranties and battery warranties are pretty much worthless. The discount is always taken off the suggested retail price, not a discounted price. You can normally easily find 25% off a tire or battery using online advertised prices. Which pretty much makes your warranty discount price worthless at this level.

    As for your battery, I think if it tests good, you should be fine. No need to replace it just yet
     
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  3. Tombukt2

    Tombukt2 Active Member

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    They said it looks good . So do I . You think it tested half in the cranking after CCA that would be around 285 is rated so half of that would be well half of that not good. Bought in 2016 and driven 30 minutes a week since 2016 is past time to change that maybe it's time to go back to a gas Yaris because driving like that I'm surprised the car is still available to be used and works seriously.byt glad it is I guess.
     
  4. Finite Resources

    Finite Resources New Member

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    Sorry, I left off some detail there. Battery was last changed in 2016, I bought the car in 2017 and drove it pretty regularly. Just very infrequent driving during covid times. I added 22K miles since I bought it in 2017 so overall I'm not someone who drives a lot compared to the averages.

    Thank you for your replies. I'll just keep any eye on it and the next time it fails battery testing from some automotive store, I'll put in a new battery and maintain better battery maintenance procedures.
     
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  5. dig4dirt

    dig4dirt MoonGlow

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    Having the smart charger will make it last longer...."smart" move.

    Nothing is wrong atm.

    My battery is oem og, so it is 8 years old.
    Was putting on 5k/yr now im at 2k or so.
    Every weekend I slap on the charger and all good.
     
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  6. 3PriusMike

    3PriusMike Prius owner since 2000, Tesla M3 2018

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    My PIP 12v battery is original and will be 10 years old in a couple of months.

    Mike
     
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  7. JC91006

    JC91006 Senior Member

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    Well if you plan on keeping it for another 5+ years, best you change it out now. You have time to shop for the best battery and select a good time for you to replace it. No need to press your luck until the part actually gives up and leaves you stranded without many options.
     
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  8. Finite Resources

    Finite Resources New Member

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    Hypothetically, if there's an awesome battery deal and I buy it, how long can I keep it around just sitting in my home? I know it would have to be on battery charger once in a while but other than that any cons here? This is assuming you know that your current battery is getting weaker and weaker and you'd be good to go with replacement without any hassle with the backup battery in your home.
     
  9. 3PriusMike

    3PriusMike Prius owner since 2000, Tesla M3 2018

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    This is my 4th Prius...only 1 ever replaced...except if you count FOB batteries.
    That was in my 2004 and only happened because a door was left open and it drained the ~7 yr old 12v battery.
    My Model 3 is my primary car so I'll just wait until the 12v PIP battery fails.

    Mike
     
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  10. bisco

    bisco cookie crumbler

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    my 12v died at 8 years while on the road, and i had to call triple a :unsure:
     
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  11. JC91006

    JC91006 Senior Member

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    You don't need to keep a new battery in your garage, install it. It seems like it's going to happen once during your ownership, why wait? If you do it now, it'll be good for another 8+ years. You most likely won't have to do this again after the 1 time. No reason to wait, you'll need to do with down the road (unless you sell the car).

    One breakdown/inconvenience will cost you more than what you're planning to save in the future. Whether you breakdown in a bad neighborhood, or you call triple AAA and they jump start the car incorrectly. Bad things happen when things occur when you don't plan for them
     
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  12. ChapmanF

    ChapmanF Senior Member

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    I handle 12 volt battery issues, if ever, by starting the car using the jump pack I have planned for, then buying a replacement battery if needed.
     
  13. vvillovv

    vvillovv Senior Member

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    Yes - pretty much ! Since you asked you might want to do the other two as well and compare the results,
    That way if it happens again to your now 6 year old 12 volt battery you have a good reference point to use any of the three ways of checking it.
    With a smart charger and using your intuition about when to check the battery voltage, the battery in your car could last 6 more years or longer. Imagine a 12 year old 12 volt battery in a Prius. It could happen !
     
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  14. Finite Resources

    Finite Resources New Member

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    Since it was 26 degrees this morning I thought I could just do that.
    • Multimeter near the battery terminals - 12.12v
    • MFD - 11.7v
    • Smart charger hookup start voltage - 12.5v
    • Smart charger ended with full charge - 14.8v (~ 15-20 mins)
    • Multimeter near the battery terminals after battery charger reported full charge - 12.4v
    • MFD after battery charger reported full charge - 11.7v
    No idea what to make out of these numbers :|

    I either got a bad smart charger, or the digital multimeter is off, or my battery is just in a weird state. I'll just go ahead and start looking for a replacement. Now the questions is do I return the smart charger...
     
  15. vvillovv

    vvillovv Senior Member

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    Really only time will tell.
    You have to remember a few things about taking voltage reading of the 12 volt in a prius that are different from most other cars.
    Opening the door wakes up the computers
    MFD - MID screens are on while in ACC - READY so that is more drain on the 12 volt.
    It's normal for the 12 volt reading to drop quickly after removing the charger.

    A good and easy way to check the 12 volt in a prius

    Take initial 12 volt reading at the battery
    Than put the prisu in ACC mode and take readings at the battery the jump points and MFD
    while still in maintenance mode
    Take readings with the headlights on and compare.
    Turn on the high beams and compare readings.
    Turn on the heater/AC fan to high.
    Push on the brake pedal and watch the MFD voltage. ( the reading should only drop while the brake booster pump runs ).

    For now, I wouldn't worry about the charger only taking a half hour to charge the battery, especially since you had the batter load tested, you ran the car which also charged the battery and all three load tests passed.

    It would be a good idea to take readings every once in a while when you've got a few extra minute on your hands. The diffs of the readings will start to make more sense.
     
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