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Battery.

Discussion in 'General Supra Topics' started by John8, Mar 3, 2020.

  1. JasonO

    JasonO Well-Known Member

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    I already have, but let me try again.

    They put it on an external charger. That charger is not governed by the system so it can charge over the 80% limit of the BMW battery registration. The BMW charger in the car doesn’t necessarily charge at full current and will allow some discharge within reason. The battery is taking charge, the car isn’t charging it to your liking.

    My own anecdote. My battery from time to time if I turn the car off at the wrong time not have a high enough capacity for my signal generator to recognize the startup signal so it will fail to turn on my amplifier. This happens once out of thirty times at worst. This points to the charging system is controlling charge current and will only get aggressive on charging at lower battery voltage levels. You don’t see me shitting bricks over this and I’m an engineer involved with lead acid battery systems.

    Like I said, IMO, you only deserve a new battery because they promised you one, not from the metrics as they are shit metrics. You absolutely may have a battery with less life, but I wouldn’t trust the data points you are giving to make that call. The system is meant to trend and alarm in absolutely concerning conditions, not make a snapshot based decision about marginal losses.
     
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  2. OP
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    John8

    John8 Well-Known Member

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    Ok, the norm is 80% charge as set by the alternator system and electronics involved. If the car sits, say for 6 months or a year (we some times go out of country to do work abroad (I do medical work and do visual documentation), how do you trickle charge it, since this will often bring it to or near 100%, since the trickle charger doesn't have the programming the car does?
     
  3. Grendel-13

    Grendel-13 Active Member

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  4. JasonO

    JasonO Well-Known Member

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    You can still trickle charge it. The battery maintenance system of the car will just hold off or reduce charging until it feels it needs to.

    I’m intimately familiar with a similar stationary system (not the BMW one) and it wants to hold the battery around 70% (for extended life) and will not charge above 80%. It will not commence charging until 60%. There are some caveats with it, but that is the gist of it. If I had to guess from what I’ve read of the BMW system, as I had similar concerns that you had, it wants to hold the battery at 70-80% but does not charge the system until it is somewhat lower than that.

    In general, light discharges and recharges are better for AGM product than deep discharges or constant charges.
     
  5. Tkoch86

    Tkoch86 Well-Known Member

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    Mine is doing that, while locked...they did some recall update on the rear camera and I think screwed up the update. When one is done it updates all systems. They didn’t seem to know what they were doing... the temp and fuel and the tach numbers. Also the hazard button. Been on for like 20 minutes now.
     
  6. akasonny

    akasonny Well-Known Member

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    Others may want to confirm but I've been told the battery (for some odd reason) is considered fully charged at 80%...by design.

    Where in Bimmerlcode do you see the charge state of the battery?
     
  7. OP
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    John8

    John8 Well-Known Member

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    Yes, after finding this out myself, I called a few BMW dealerships. One said they had never heard of that and of course, it should be charged to 100%. Another large BMW dealership in Calif. (manager) said, it was correct, they only charge to 80%. He had asked one of the top people why, when they were visited by BMW, and they would not tell him! But he confirmed that the batteries only are charged to 80%. Mine charges up to 82% and that is it.
     
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  8. akasonny

    akasonny Well-Known Member

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    The Supra uses AGM batteries.
     
  9. akasonny

    akasonny Well-Known Member

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    Mine was dead on the dealer's showroom...much to the chagrin of the embarrassed salesman. They couldn't release the car to me saying that BMW has to reprogram all ECUs...not just a charge. I was told they'd replace the battery. They didn't. They simply recharged, re-calibrated and delivered the car to my front door 2 days later. I've had considerable concerns over this issue...and documented the situation.

    I haven't had any noticeable problems since though I suspect that condition shortened the battery's lifespan. I was careful to buy a charger with a specific AGM charge (I believe long-term use of a non-AGM charger is a bad idea).
     
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  10. XtremeMaC

    XtremeMaC Well-Known Member

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    I don't know much about the AGM batteries, but Lithium Ion / Nickel / Po.. etc. batteries which are commonly found in everyday devices (laptop, phone, etc.) always advised against fully charging. Most laptops do say though, if you keep it plugged in all the time, let the battery charge up to 80% (controlled via software), but seeing how phones are frequently replaced and charged every night, they're a different story than car batteries, but chemically they're similar enough to say don't let charge go down below 20% and charge over 80%...
    yet again, software controlled devices show that it's 100% charged where in fact they're 80% to improve health/longevity.. Sounds like BMW is using this software control idea as well...
     
  11. puzzled

    puzzled Well-Known Member

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    Has anyone found a good way to wire the battery tender from under the trunk? I don't drive my Supra all that much and have been routing the cord from under the engine bay into the charge posts in the front using alligator clips. This way I can keep the hood closed completely and enjoy the beautiful car while parked in the garage.

    Since I will be disconnecting the battery temporarily to install paddles, I would like to wire the umbilical cord at the same time directly on the battery terminals, and drop the umbilical cord under the trunk so that I can plug it from under the car without opening anything.

    My car will never see snow nor rain so not really worried about water although I will take precautions to place in a dry location.
     
  12. XtremeMaC

    XtremeMaC Well-Known Member

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    slightly off topic: There are several people in the forum with depleted batteries getting error messages... I don't remember right now if that's because ECU is getting lower voltage than ideal or if for some reason ECU doesn't like disconnects or cannot recognize new battery or whatever. You gotta be able to disconnect the battery. Chances are I'm misreading this whole thing :hmm::confused:
     
  13. OP
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    John8

    John8 Well-Known Member

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    Mine was dead on the showroom floor, the day before I came back to see it again. They told me they replaced the battery. They lied, I found out later. I asked for the paper work and they admitted the recharged it but said, "it is under warranty". I hate lying and I lost most all confidence in them. This is main dealer in Tucson.
     
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  14. puzzled

    puzzled Well-Known Member

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    I read another thread about not connecting the tender directly to the battery so scratch my idea. I wish there was a safe way to plug the car in from under the car without needing to open the hood each time.

    As for unplugging and plugging the battery, I think if you do it in one shot on a charged battery you'll be fine. It's usually when there's insufficient power and people open doors or what not, the fluctuation in current causes the errors.
     
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  15. akasonny

    akasonny Well-Known Member

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    This happened to me too. I live in Tucson but bought the car in Phoenix. That dealership promised a new battery but, later, said they recharged it. Argh!
     

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