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Using Battery Maintainer on 12V battery when in storage

Discussion in 'Model 3: Battery & Charging' started by QuincyPS, Aug 25, 2020.

  1. QuincyPS

    QuincyPS New Member

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    A general manager at Tesla service recommended employing a battery maintainer when my car is in storage for 3 months. I picked up a Schumacher 1.5 A but wondered if A) Amp is enough B) If I need a lithium retainer (vs standard AGM deep-cycle). The car will be in a garage in dessert end of August thru mid-November. Welcome your thoughts.
     
  2. miimura

    miimura Well-Known Member

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  3. QuincyPS

    QuincyPS New Member

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    Thanks. Just to clarify; Standard AGM deep cycle maintainer is OK but recommended A is 3.5 - 5. Yes?
     
  4. QuincyPS

    QuincyPS New Member

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    Thanks. Will check it out.
     
  5. jmaddr

    jmaddr Member

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    Will it be plugged in during the storage period?

    if so, I’m confused as to the reason why Tesla recommended that. You have a large battery whose main purpose when not driving is to keep that 12V battery at a sufficient charge. In fact, it’s not like we have an alternator to charge the battery when driving. When driving, the same charging circuits are active as when in storage.

    The ONLY difference I can think of is when the main battery is below a certain level (20%) it doesn’t charge the 12V so it might be a good thing to have a trickle charger. So if you have to store you WITHOUT having it plugged in, the topping off the 12V might not drain the main battery as quickly, but we have to be taking weeks upon weeks here. 3 weeks should be no problem if you are either plugged in or start with a decent charge and turn off the ancillaries like sentry and summon.
     
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  6. pjensen

    pjensen Member

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    Typically unused lead acid batteries will sulfate and can be destroyed (over time). There are trickle chargers (battery minder) that restore sulfated batteries. I have recovered many failed batteries by using a battery minder (adding several years to their life).

    Though I would not want to hook up a trickle charger to a battery that already is being actively being charged by the car's electronics/computer. That might damage something - and it wouldn't be the trickle charger.

    Perhaps ask the tesla manager for a clarification - how to do it.
     
  7. jjrandorin

    jjrandorin Another BMW convert

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    the thing that confuses me about this recommendation from tesla, is that if you could plug in a battery trickle charger somewhere, you could plug in the car charger instead into the same outlet. Since the HV battery charges the 12v when plugged in, I cant see any benefit for using a trickle charger on a tesla (Because of the above).

    Am I wrong in my understanding that the HV charges the 12v? If not, am I wrong in assuming that if one could plug in a trickle charger to an outlet? If neither of those are wrong, what would be the point of a trickle charger?

    (real question)

    I know what they are for, as I have one for my BMW, but I cant think of why one would be needed on Model 3.
     
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  8. electrongeek

    electrongeek Metrology Fanboy

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    When all of the TM3 electronics are fired up, they seem to suck about 300 watts. I surmise that the TM3 has a way to check 12 Volt battery voltage without fully powering on, since 300 watts takes about 13 amps from the 12 Volt battery. It looks like when the 12 Volt battery falls to about 12.75 Volts, the car will initiate a charge cycle with a maximum of 14.4 Volts, until it detects that current has fallen enough to indicate full charge and it is time to terminate. Then the battery voltage will slowly fall as surface charge dissipates, and other current draws bring it back down to 12.75 Volts, when the cycle is repeated.

    Now, if you put a battery maintain on that 12 Volt battery, it should be able to keep the voltage at about 13.4 Volts, a good float level. Even a low current batty maintainer should be able to keep it here, short of the car's electronics being full on. If it can do this, it may satisfy the car that it does not need to fire everything up to once again apply a 14.40 Volt charge to the battery. If this works, it should prolong the life of the 12V battery during prolonged storage. I don't know that this will work. I'm going to give it a try at some point, using a charger and a 12 V battery voltage logger. (Keep in mind that the voltages applied to a 12 Volt battery for charging and float are normally adjusted based on battery or ambient temperature, so the numbers above may not correspond to your situation if it varies from the 75 F conditions under which I made my observations).
     
  9. Rocky_H

    Rocky_H Well-Known Member

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    While it's certainly possible to do this, it is not very important. Yes, ALL Tesla vehicles monitor the state of the 12V battery and will use the main battery pack to top it off again any time it gets low. So if you have the car plugged in, it will just take care of this itself.

    There is a very small point of usefulness here. The car can take care of this itself, the way I mentioned, but that is putting the 12V battery through cycles of low/recharge/low/recharge over and over. So if you do want to save some wear on the life of the 12V, you can connect it externally, and that will supply all the idle drain from the onboard computers, and then it will just never drain low, and the car will never detect any need to refill it. There's a long thread about this from a few years ago in the Model S section. Numbers and location for connections will be a little different but principles will be similar.

    Any reason not to hook up a battery tender to the 12 volt battery ?
     
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  10. camalaio

    camalaio Active Member

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    3 months eh?

    You'll really want to have the car plugged in, i.e. be charging the car. Not just the 12V battery.

    Depending on your settings, even a fully charged battery (which isn't recommended for storage anyways, more like 60%) may not last unplugged for 3 months. You'd have to disable darn near everything you can, never "check on it" via the app, and make sure it's stored somewhere where the temps are somewhat controlled (32F - 100F or so). Then it might be OK upon return.

    But if you can plug in a battery tender, hopefully you can also plug in the car (maybe it's not feasible due to a shared circuit or something?).

    Standby drain according to the Stats app, when plugged in, works out to about 60W average. This will be mostly the 12V system, and implies you'd need a 5A charger. However, leaving it unplugged and turning off a bunch of features, this drops to about 11-14W. The 1.5A charger would be sufficient in this case.

    I'd be curious if just keeping the 12V battery topped would prevent drain on the HV battery that has been otherwise noted (it should), but you probably don't want to be the guinea pig on that. But if Tesla service recommended it to you, then... hey, why not? (peace of mind, that's why)

    I expected this response from someone much sooner, heh. It's possible they're storing on a shared circuit that plugging in the charger would trip a breaker or something.

    I can see benefits, but they're small and I'd still be concerned about the HV battery state over time. It's a risky bet, if probably a safe one. Keeping the 12V topped up should prevent drain from the HV battery, while keeping the 12V battery happier overall.

    The "should prevent drain from the HV battery" comes with so many caveats though. They're all possible to deal with, but I'd fear not accounting for something.
     
  11. Rocky_H

    Rocky_H Well-Known Member

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    Well, that's the interesting thing from that thread I linked.
    Not just mostly--it's all the drain. The main pack has almost no loss at all for months.
    Not a guinea pig--tested and confirmed in that thread I linked. But it does take a tender with a decently high amp output, like 4 or 5. Most tenders are built with the expectation of being on a regular unused idle battery, where it hardly needs anything, rather than this case where there is a noticeable steady draw on it.
    So yes, if you use a 12V tender with high enough amps to cover the vampire drain, the high voltage pack just won't lose energy or need recharging for many months.
     
  12. QuincyPS

    QuincyPS New Member

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    Again, Thanks for all the great input and advice. I was not able to follow up with the general manager at Tesla for further clarification on trickle recommendation. My guess is that it would help prolong the life of the 12V battery and perhaps act as back up for an outage. His recommendation was to use both battery maintainer while also charging the car at 50%. After reviewing all the valuable input from above I decided I needed to really dive into this but don't have the time as I am leaving in 24 hours. So I asked another Tesla owner to take out my car once a month and drive it around. This is the least technical solution but most practical at this moment.
     
  13. Rocky_H

    Rocky_H Well-Known Member

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    That's neither solution and is directly the gas car mindset for how their 12V battery system works, where it needs to be driven around to refill the 12V battery with the alternator.

    With the Teslas' electronics idle drain, it's going to drain down that 12V battery in a day or two and be topped off from the main pack frequently. So if you are only having someone drive it around once a month, it's going to get refilled off the main pack 29 out of 30 days anyway, so that's not really accomplishing anything. Either you put a real tender on it, or there's just no need to do anything else at all but leave the car plugged in.
     
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  14. Gasaraki

    Gasaraki Member

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    Yeah I don't get this. The car is maintaining the charge of the 12V battery so if you plug in the car to the 120V outlet and set the charge to 50%, the 12V battery is maintained also.
     
  15. electrongeek

    electrongeek Metrology Fanboy

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    When the car is plugged in, it maintains the 12V battery by waiting for current draws to bring the battery voltage down to around 12.75 V, then initiates a 14.4 V charge. What it doesn't do is maintain the battery at what is considered an ideal "float" voltage. Cycling a 12V battery like this cuts into its useful life. How much, we don't know. Maybe an insignificant amount, but if the car is going to be in prolonged storage why not reduce this constant cycling? It can only help.
     
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  16. Rocky_H

    Rocky_H Well-Known Member

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    From what I have seen, very significantly. Lead acid batteries can last many years if you are just keeping them at a steady topped up state instead of only lasting for 2 or 3 years as these do with a lot of up and down cycling. So if you are putting it on a tender in your garage all the time, that battery hardly ever goes through any cycles and will easily last double or triple as long. But it's kind of a lot of hassle to do it often enough to help, so it's not worth the bother for most people.
     
  17. grmdl3

    grmdl3 Member

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    Pretty. much anecdote, not data, but...

    FWIW I went through a series of AGM batteries on my Unimog (there were 4 Optimas in there) which was stored for long periods without running. I used trickle chargers on them to try to keep them healthy. Those batteries seemed to all die early deaths.

    I was talking to one guy from Johnson Controls awhile back, and he said that those chargers actually contribute to sulfate crystals forming and penetrating the membrane between cells. His recommendation was to leave the battery as-is, then once a month or two hook it up to a charger to top it off.
     
  18. electrongeek

    electrongeek Metrology Fanboy

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    Sulfation of lead acid cells does not occur when fully charged. If, however a battery of cells (e.g. the 6 cells in a 12V battery) in a lead acid battery never sees a voltage above the ideal "float" voltage of about 13.4V, then there is a good chance one or more of the cells will eventually find itself undercharged and subsequently be subject to sulfation. So yes, a periodic high voltage charge will bring those laggard cells up to full charge to reduce the chance of sulfation, and never charging the 12V battery above 13.4 V or so can lead to cells becoming sulfated and losing capacity. If you are storing a battery that has no load on it, I would agree a "trickle" charger is not needed and an occasional (interval depending on the temperature they are stored at) full charge is best. That isn't what the Tesla 12V battery sees however. If you want to see how a Model 3 12V battery is voltage cycled, I've posted a graph of that in another thread here a week ago.
     
  19. CyberGus

    CyberGus Not Just a Member

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    Regardless, I would leave the frunk open, just in case ;-)
     

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