12 volt lithium replacement battery by Ohmmu

Discussion in 'Prime Main Forum (2017-Current)' started by Mark in NY, Apr 20, 2021.

  1. Mark in NY

    Mark in NY Junior Member

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    No problem with the car operation yet but I was puzzled by the 11.6 volt battery voltage I measured one morning. I then measured a substantial reduction in capacity of this original 2017 Prime 12 volt battery per a Snap-On battery tester. Looked around to get a heads-up on available replacement battery before I had a non-starting Prius. My first thought was to get an Optima unit but they do not make a battery suitable for the new gen 4 layout (larger battery in the engine compartment). After getting frustrated seeing some confusion in parts listings and rather high prices for the few plain old lead acid batteries available in this unpopular size I searched around and also through the threads on Prius Chat. Came across the Lithium replacement by Ohmmu. Contacted Ohmmu and they answered several questions I had about a lead acid to lithium swap-out in the Prime. Well I did not wait for the OEM battery to degrade further, took the plunge and bought a lithium replacement at one third the weight of the lead battery. Pricey but supposed to last much longer.
    Toyota Prius 12V | ohmmu.com
    Installed it today and operation is fine. Voltage about one volt over the lead acid battery. Over13 initially. I am curious to see what it stabilizes at after a few weeks of use.
    Installation via a strap that came with the battery and 2 small spacers I added to secure the smaller battery in the tray.
     
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  2. Salamander_King

    Salamander_King Senior Member

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    Interested to find out your long-term follow-up. At $349.00, the cost is almost three times the regular 12v lead-acid replacement battery for the Prime (or Gen4). If it only lasts twice as long as regular lead-acid, as advertised, then it may not be very cost-effective. But with 5 years full-replacement warranty, you may be OK. Or it may last much longer than 2x regular lead-acid.
     
    #2 Salamander_King, Apr 20, 2021
    Last edited: Apr 20, 2021
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  3. jerrymildred

    jerrymildred Senior Member

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    Interesting. Please keep us posted. Those are some pretty impressive claims on the website.

    How often and how far are you driving? Zillions of people lately are having 12V failures due to not enough run time to keep the battery charged. The 12V in my 2017 Prime seems to be acting virtually new. But I drive almost every day and usually do about 200-300 miles a week.
     
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  4. Mark in NY

    Mark in NY Junior Member

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    Yes indeed, in pure dollars cost/benefit it might not be completely worth it (although I did see prices around $180 for replacement lead batteries). I went with the new tech, no acid related corrosion, more stable 13v, and loss of 20 pounds.
     
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  5. Mark in NY

    Mark in NY Junior Member

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    I drive only short distances a few times a week. Since there is no big starter drain the battery should stay pretty much fully charged. This is why I was surprised to see 11.6 volts one morning when I checked it on a whim. The capacity check results got me started looking around for a replacement just to see what was out there. Looking at the Tesla sites turns up a rather large issue of the 12v bats failing in half the time of the expected 5-7 years.
     
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  6. Salamander_King

    Salamander_King Senior Member

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    Yeah, I think the OEM 12v battery by Toyota is around that price, but you can now find aftermarket 12v at around $120. After battery core exchange, the price would be around $100. From my experience, if you are driving at least once a week for a minimum of 1 hour, the 12v battery will stay above 12.0v. Anything less, especially for the older than a few years battery, you have a chance of draining the battery below 12v and have a chance of not starting. The question is, how does the lithium battery pack handle that type of low SoC. I would think it would be better than lead-acid or AGM but I don't know.
     
  7. Mark in NY

    Mark in NY Junior Member

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    Searching though the few Tesla owner sites I find the Tesla owners who have converted to the Ohmmu, are happy with the results a year or more down the road. This included those located in both hot and cold climates.
    My multiple short trips are linked to multiple charging sessions per day as well so I was puzzled about the low voltage I measured. I thought between drive time and charge time the 12 volt bat should always be topped up. My Schneider smart automotive (lead-acid) charger interprets the OEM bat to be at 62% charge level when I hook it up.
     
    #7 Mark in NY, Apr 20, 2021
    Last edited: Apr 20, 2021
  8. road2cycle

    road2cycle Member

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    But there are parasitic drains on the battery while it’s sitting. Add to that short trips which may not fully charge the battery back up and the result is less than nominal voltage on the battery.
     
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  9. Hicksite

    Hicksite Member

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    Would the heat under the hood be a potential problem for a lithium ion battery located there?
     
  10. Mark in NY

    Mark in NY Junior Member

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    Yes and that was one of the things I was concerned about since I travel and leave the car at airport long term parking on occasion. The Ohmmu folks say they test their batteries with a more rigorous drain test than the std lead-acid spec and their bat has substantial reserve capacity. Time will tell.
    I have to say this line of thinking all started before I measured the OEM bat voltage. I replaced the lead acid bat in my grandson's powerwheels jeep last fall with a lithium unit: (amazon title)
    12V 16Ah Deep Cycle LiFePO4 Battery, 2000 Cycles Miady LFP16AH Rechargeable Battery, Maintenance-Free Battery for Golf Cart, Boat, Solar System, UPS and More …
    The jeep must have 4X the range now ! Low & behold I spend $$$ on a lithium bat for the Prime :)
     
    #10 Mark in NY, Apr 20, 2021
    Last edited: Apr 20, 2021
  11. Salamander_King

    Salamander_King Senior Member

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    Prius Prime does not really top up the 12v battery while plugged in. It only trickle-charge to maintain bearly at around 12v. And this only happens while the traction battery is actively being charged. Keeping the charging cable plugged in longer than necessary to charge the traction battery actually drains the 12v battery.
     
  12. Mark in NY

    Mark in NY Junior Member

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    I don't think it is more sensitive than a lead-acid. In addition on an annual basis the car is on battery 90% and hybrid 10% of the time. A few years back during a heat wave after driving home from work with AC on I got home, opened the hood and felt various surfaces by hand. It is essentially ambient temp under the hood ! Certainly a different world from the days of my old high output V-8's.
     
  13. jerrymildred

    jerrymildred Senior Member

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    That, I don't know for sure. I doubt it, though.

    Yup. There's what ran down the 12V. Because of what @road2cycle pointed out.

    Yup. That and the fact that the charging system doesn't charge very aggressively. So, short, infrequent drives, will demand a maintenance charge. The Lithium battery might handle it better, but it's also going to gradually run down. That's the nature of cars.
     
  14. Hicksite

    Hicksite Member

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    Thanks!
     
  15. PT Guy

    PT Guy Senior Member

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  16. MikeDee

    MikeDee Senior Member

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    Lithium batteries require a different charging regimen than lead acid. How is that addressed with this battery?
     
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  17. Mark in NY

    Mark in NY Junior Member

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    I questioned that myself. Ohmmu advises that their internal battery management system in the battery takes care of charging issues. Judging by the reviews from Tesla drivers who have posted after over a year of use it works well.
     
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  18. Hybrid Hound

    Hybrid Hound Junior Member

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    My 2015 has the original battery. I have been getting readings at the battery of 11.9-12.3. The charge seems to be staying at about 14.5 when the car is in ready. This September the battery would be 7 years old, all in the Florida heat. The best battery I could find as to CCA/price/warranty was at Batteries Plus. 219 minus 10% for online order then pickup at store. Plus sales tax and they want my old battery. I decided to go with the OHMMU Lithium after reading many reviews. 349. (Current sale price). Free shipping. No tax. I keep my old battery. When it arrives, I will do the install and after a month or so will review it here. 10 pounds less weight. If I sell or trade my car (not likely with 43K on it) I will put the old one back in with a good charge on it. Meanwhile, I can use it for emergency lights and fans with my inverter for power outages if I keep it on my battery maintainer until needed. So, I guess since the net cost difference in my case was about 139, I hope it will be a good investment. I really do like this car, and am not crazy about the style change in the next generation, so we may have it a while. And...the consistent 50+MPG has been a blessing during the pandemic since it means (for us) going to the gas station much less.
     
  19. GregersonIT

    GregersonIT Member

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    I've always done batteries plus myself. They usually have a 4 or 5 year warranty.
     
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