Battery charge program for prime - AGM?

Discussion in 'Prime Main Forum (2017-Current)' started by Professor Chaos, Apr 24, 2020.

  1. Hicksite

    Hicksite Junior Member

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    Really, "SIGH"? Are you losing patience with me? And why do you keep using all CAPS when you say "NO". Is there a reason for the extra emphasis? I don't want to misinterpret your intended tone. :)

    By "extra operation" do you mean "unnecessary operation"? If so, then it is a matter of who defines "unnecessary". I generally tend to trust the manual on that issue. And if the battery is "TOAST" it's going to have to be removed from the car anyway, right? So that probably isn't really an "extra" operation anyway.

    I do understand that under normal conditions most on here do not disconnect the battery before charging it and have never had any problems doing so. So under normal conditions that is my plan as well. But I'm not sure anyone on here has faced this particular situation, have you? So I would rather err on the side of caution and at least disconnect the ground cable.

    Probably just me being extra cautious! :)
     
  2. Salamander_King

    Salamander_King Senior Member

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    I did not disconnect 12v battery when I charged it, but the manual is being extra cautious as you are to prevent potential damage to electrical system in the car by reverse polarity. But if you are careful, charging the battery without removing is perfectly safe, IMHO. Most chargers have built-in reverse polarity protection.
     
  3. Hicksite

    Hicksite Junior Member

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    Thanks, yes I have normally charged with the battery connected with other cars and will also do so with the Prime. It was just this particular circumstance where I thought it might be worth taking the extra precaution.
     
  4. Salamander_King

    Salamander_King Senior Member

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    Yeah, replacing just a damaged 12v is much cheaper than repairing damaged hybrid system electronics in the car for sure.
     
  5. Washingtonian

    Washingtonian Active Member

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    I had a similar problem last week with the 12V battery in my 4Runner. I hadn't used it for awhile and it was completely dead. I have an older conventional charger with settings of automatic, manual, 2Amp and 12Amp. Set it on auto, 12A and it didn't want to charge. Changed to manual, 12A and it eventually fully charged. With it charged, I noticed that I had left the parking lights on; the reason for the total discharge. Anyway, the battery seems to be perfectly fine now. Just took a fairly high current charge to rejuvenate it.
     
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  6. Mendel Leisk

    Mendel Leisk Senior Member

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    I suspect the reason smart chargers don't work is because they do a rudimentary assesment, decide the battery is toast, not worth charging. Best to replace, before you're stuck. But who knows.
     
  7. thymara

    thymara Junior Member

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    I leave the battery connected and use the picture from the manual on how to do the connections
     

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  8. Rob43

    Rob43 Senior Member

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    Sounds almost exactly like what I proposed in post #3,...Congrats on your success !



    Rob43
     
  9. Salamander_King

    Salamander_King Senior Member

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    That diagram is from the manual for jump starting Prius using another car. I guess it is safer than connecting to both + and - post. Did you have to remove the plastic engine cover?
     
  10. thymara

    thymara Junior Member

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    I did take off the cover, 1st time off I had to work at it, there are 3 posts that provide the connection, 2 on the top (L,R) and one bottom middle
     
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  11. Professor Chaos

    Professor Chaos Junior Member

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    OP here, thought I'd provide an update. To recap, the battery was dead enough that it wasn't recognized by the CTEK at first, but after a jump and about 20 minutes of running the CTEK would recognize it. I didn't think to take voltages before or after the jump.

    I let the CTEK run the whole charging program (including a reconditioning step). Then I tested the battery voltage after starting up in ON mode, running the high beams for 30 seconds, and then shutting off the car. The battery started at 12.6 V immediately after the headlights shut off and drifted up to 12.9 V within a minute.

    Repeating the test after letting the car sit (i.e., not charging) for 24 hours, the battery started at 12.3 V immediately after the headlights shut off and drifted up to 12.7 V.

    Promising? I'll let it go another day and see, though at some point I'll take it in for a CCA test... getting stuff like that done is never trivial in San Francisco.
     
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  12. Rob43

    Rob43 Senior Member

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    Yes, very promising, good job !

    I Strongly Recommend that you re-charge your 12v battery with your CTEK again in about ~7 days. After that I'd tell you to re-charge at your convenience once every month or two.


    Rob43
     
  13. sam spade 2

    sam spade 2 Senior Member

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    Guess I didn't finish the thought.............

    It usually won't take but a few minutes to cram enough charge into it so that the tender will take over.
    But if it does draw near to the max. capacity of the charger for much more than 10 minutes......then you might as well give up and look for a new one.

    Letting it charge at 10 amps for HOURS might indeed cause some additional damage.
    But the key word is "additional" because taking a high charge like that for a long time is a good indication that the battery is shot already.
     
  14. sam spade 2

    sam spade 2 Senior Member

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    True but.......how many times have people done that and had their battery pronounced "good" only to find out that it really is NOT ???
    That happens a lot more often than it should.
     
  15. Washingtonian

    Washingtonian Active Member

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    I would think the opposite would be more likely. Their incentive is to sell you a new battery.
     
  16. sam spade 2

    sam spade 2 Senior Member

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    I don't know WHY but it seems that auto PARTS dealers aren't as dishonest as the service places are.

    In the case of testing batteries, they just simply don't have good equipment.......or don't really know how to use it.

    Identifying a BAD battery is easy. Telling when one is marginal or intermittent is MUCH harder.
     
  17. thymara

    thymara Junior Member

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    In the past 14 days I've driven my Prime on 1 day for 20KM, all EV. At no time have I connected my 12-volt charger. Voltage and voltage change are shown for each day.
     

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  18. bisco

    bisco cookie crumbler

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    that looks pretty normal. what day did you drive?
     
  19. thymara

    thymara Junior Member

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    2020-05-16. Had to shuttle the daughter back and forth to get her winter tires changed for summer.
     
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  20. bisco

    bisco cookie crumbler

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    it will be interesting to see how low it goes before the next time you drive it. i assume the sks shut itself off after 5 days.
     
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