2018 Prius C 12V Battery

Discussion in 'Prius c Technical Discussion' started by NJ2018PRIUSC, Mar 4, 2021.

  1. NJ2018PRIUSC

    NJ2018PRIUSC Junior Member

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    New forum member here.

    Our 2018 Prius C grocery getter, purchased new 12/2017 has 7200mi and had been largely idle (< 300mi) since the pandemic began about a year ago. We are retired and only need the car for very occasional outings (e.g., necessary Dr. appointments) and potential emergencies.

    This week, we were heading to the park for a walk and the 12V didn’t have a sufficient charge to start the car. The small screen on the upper part of the dash showed the outline of the car as well as the check engine light and the horn would work, but weakly. I pulled the battery, following the owners’s manual directions, and it reads 8.1 V across the terminals and ordered a 1.25A Battery Tender Plus, which I’ll have by the weekend. From what I’ve read, I’m assuming that the 12V battery is probably nearing the end of its service life (time-wise though it’s a very low mileage car - probably too low to have justified the cost of the hybrid in the first place...), so I found a store that will ship an OEM battery, which I’ll have next week.

    If there will be more than a couple of days between the arrival of the tender and the OEM battery, I plan to charge the original and reinstall in case we need the car for an emergency.

    I’m assuming the OEM battery is AGM. Is this correct? It’s not labeled as such as far as I can tell.

    Yuasa AGM batteries are shipped factory-activated (and charged) or with a bottle of electrolyte. Does any one know which is the case for this battery? I activated my share of batteries during my motorcycling days, but it’s not my favorite procedure.

    Any other tips or words of wisdom would be appreciated. I obviously need to drive the car more frequently.

    Thanks!
     
  2. NJ2018PRIUSC

    NJ2018PRIUSC Junior Member

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    One thing I neglected to mention is that a 3-4 weeks ago, I used a portable air pump powered by the accessory port to add air to all 5 tires. It took about 20 min. I obviously should have left the car in READY for a while after, but I was cold and not thinking clearly. The car hasn’t been run since. It’s seems likely this was the final insult before the 12V battery lost sufficient charge to get the car going.
     
  3. PriusII&C

    PriusII&C Member

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    I am not sure what kind of auxiliary battery a 2018 has. I have a 2012. It has an AGM battery. It has been parked since May of last year. For every 3 weeks, I just turn on the car for 20 - 30 minutes. The original battery still works fine.

    The capacity of the auxiliary battery on the 2012 is pretty small, 35 AH. So it is probably a good idea to keep the car on when you use the battery to do other things.

    If you don't run the car much, it is a good idea to keep the battery charged. From what I have read, it is better to use a smart charger than using a trickle charger. AGM batteries are more sensitive to over charging than flooded lead acid batteries.

    I would expect the new battery be factory charged. It should be ready to use when arrived. But you may still want to get it fully charged since either the factory may have not fully charged it, or it may have lost some charge on shelf or during shipping. SOC maybe is not near 100%.

    Besides the auxiliary battery, pay attention to the hybrid battery. If its SOC gets too low, you may have a much bigger problem.
     
  4. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Yep it's a vented AGM. Not much reserve capacity. We've never had a problem with ours despite a similar sharp drop in use- but my tire inflator runs on detachable bricks it shares with the lawnmower. I had it in my head that I'd be (preventatively) replacing our 12v in the spring or summer of 2022. Were I to severely discharge it during current cold weather I'd replace it straight off.

    The ones sold by Toyota are fully prepped, load-ready. Can't speak for any others.

    Sounds like you've got both short term and long term plans set to go, just waiting for the mailman.
     
  5. topshot

    topshot Member

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    That's a pretty short life for an OEM12V IMHO though you don't drive much to keep it charged apparently. Running a compressor for 20 min in colder temps pushed it too low to power the computers but the tender will recover it from a discharge like that. It's getting time for most 2015s to replace theirs. I will be this summer.

    Driving so little I'd be more worried about the traction battery. The Prius is not meant to be driven little. If you know you won't be driving for a few weeks then make sure you're at least half on the gauge when you power down. A newer one like yours should have no trouble holding charge. If you leave it set for weeks on its normal low charge state (i.e., just before engine would kick in to charge it) it is possible of not having enough power to start the engine, especially if it is cold.
     
  6. NJ2018PRIUSC

    NJ2018PRIUSC Junior Member

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    Thanks to everyone so far!

    Any additional thoughts about whether or not the original battery can be recovered in the short term? Just wondering in case there is an issue with the new one and whether or not it’s worth reinstalling in the interim for emergency purposes.

    Is it better to charge the new battery on the Battery Tender or just install and let the car do the work?

    Is there any issue with leaving the Battery
    Tender with the ring terminals attached to the battery when it’s installed to facilitate any maintenance charging? The reason I’m asking is this that owner’s manual states that the ground should be disconnected from the battery terminal if charging the battery in the car. The ring terminals would be attached to the bolt on the battery cable, so disconnecting the ground wouldn’t allow for charging.

    I also bought a Noco GB70 for jump starting. Any issues I should know about? I can’t tell if the cables are long enough to attach to both jump points, but took a chance on it anyway.

    re: hybrid battery and little driving
    This car replaced an 11 year old Honda Fit with only 40,000mi. The primary reason we bought the Prius C was for the safety features and decent crash test results at the time. The hybrid was an extra ‘bonus’ (and we like the car!) but I should have done more research as a gas-only car would have been a better choice and more cost-effective given our limited driving, which won’t change much from before the pandemic. If things are back to normal(ish), we may sell it before next winter and buy a gas-only car. Or branch out and take more trips. ;)

    Thanks again!
     
    #6 NJ2018PRIUSC, Mar 5, 2021
    Last edited: Mar 5, 2021
  7. sam spade 2

    sam spade 2 Senior Member

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    You should NOT count on using the original battery for actual driving again......ever. It likely will leave you stranded.

    Your new battery MUST be fully charged before being used. That can be done in or out of the car.
    Your BT Jr. should handle that fine but it might take a LONG time.......like 12 hours.

    The "pig tail" for the charger can be left attached as long as it won't get pinched or otherwise shorted out.
    If the vehicle is parked where there is power available, just leave the tender connected when not in use.
    That is how it is made to be used.

    AND, I just have to ask: Why in the world would you have a battery shipped to you instead of getting one at a local shop ?
    There are several potential problems with "mail order", including what happens if your new battery ends up being bad ??
     
  8. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    For the battery's sake, I don't think there is a significant difference between your charging choices. If you choose to do it by leaving the car in READY mode, I'd wager that you would hit your 12v state-of-charge goal sooner than if you hooked up the tender.

    I don't think you'll see any difference between the car sitting in READY mode in the driveway and actually being driven around. The 12V charging system is not dependent on engine RPM.

    If I understand you correctly, you want to install the terminals permanently on the battery and then periodically connect the tender by way of a quick-disconnect connector further up that wire?

    If so, the only problem I can see is an electrical safety hazard on the + wire itself- it should have a fuse in the line as close to the battery terminal as possible. Even though you aren't planning on using the cable in transit, you don't want to risk fire from that hot wire being pinched up against a (grounded) chassis part in a crash.

    So if there isn't an inline fuse close to the battery end, add one and you should be set.
     
  9. NJ2018PRIUSC

    NJ2018PRIUSC Junior Member

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    re: old battery
    What I assumed. Wishful thinking. I’ll charge, reinstall and only use the car in dire emergency. I don’t need it for regular use.

    re: pigtail
    I did this with motorcycles, but it contradicts the instructions in the owners manual which calls for disconnecting the ground at the battery terminal, which would then disconnect the attached ground cable of the pigtail.

    re: shipping
    Good question! Pandemic. I live in a high risk household and we’re not yet vaccinated, so I can’t visit a shop, the local dealer can’t/won’t deliver (or ship for that matter) and I don’t have other transportation in any event. Mail order was the best I could do under the circumstances, knowing the risks. If the new battery is bad, it’s bad and I’ll have to try again or find another solution. The cost of the battery (and potential loss of $) can’t be high priority right now.
     
    #9 NJ2018PRIUSC, Mar 6, 2021
    Last edited: Mar 6, 2021
  10. NJ2018PRIUSC

    NJ2018PRIUSC Junior Member

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    The cable does have an inline fuse. Thanks.
     
  11. NJ2018PRIUSC

    NJ2018PRIUSC Junior Member

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    The original battery has been charged and reinstalled. The car will stay put, barring an emergency, until I have the new one. The traction battery gauge registered well over half when I fired up the car and the engine only ran for a few min in READY for an hour. 12.67V at the terminals after the car sat for a bit with the key out of the ignition. So, that battery isn’t heathy (no surprise).

    Does anyone recommend a specific battery load tester that they’ve used and liked? Would that tell me much more than a multi-meter given how the battery is used in this application? The battery is rated CCA 240A on the label. Preferably something with large, easy to read display. I’ve developed an interest in this and would like to keep a better watch on things going forward.

    Thanks.
     
    #11 NJ2018PRIUSC, Mar 11, 2021
    Last edited: Mar 11, 2021
  12. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    I'd love to recommend the $20 analog cen-tech model from harbor freight because it's cheap, reliable, and easy to use. Unfortunately it isn't very accurate when used on a battery as small as what's in the Prius- the default load it presents is a bit too big, and the meter scale isn't well calibrated for the lower range.

    AGM batteries have a very low internal resistance that can lead to false results with digital battery analyzers unless they have a compensation applied. Look for a tester that specifically says it can do AGM.

    I imagine you would do best with a motorcycle battery analyzer because they're going to be in the same capacity range- I just don't have any direct experience with any.
     
  13. sam spade 2

    sam spade 2 Senior Member

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    A voltmeter really is good enough if you use it right.
    IF it is sitting unused and totally OFF, and you see the voltage continues to slowly drop over a short period like maybe 7 days until it gets down to 12 or less........then the battery has failed. And likely won't "start" the car again.

    There is little else that you need to know.
    "Watching" it with a different kind of tester accomplishes little to nothing useful.
     
  14. RobAustin

    RobAustin Member

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    A fun and easy way to monitor your 12v system voltage: use a "cigarette lighter LED voltmeter" Amazon has them for $10-15
     
  15. sam spade 2

    sam spade 2 Senior Member

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    With most modern cars, that only allows you to easily monitor the CHARGING voltage, since that power socket is disconnected when the car of OFF. In that case, it tells you pretty much nothing about the battery itself.
     
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  16. NJ2018PRIUSC

    NJ2018PRIUSC Junior Member

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    Makes sense. Thanks.
     
  17. RobAustin

    RobAustin Member

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    True.

    But... the Accesory mode energizes the power outlet w/o the charging voltage from the DC/DC inverter.


    From the owners manual:
    ...The “POWER” switch is in ACCESSORY or ON mode. ■ To prevent 12-volt battery discharge Do not use the power outlet longer than necessary when the hybrid system is off.
     
    #17 RobAustin, Mar 14, 2021
    Last edited: Mar 14, 2021
  18. NJ2018PRIUSC

    NJ2018PRIUSC Junior Member

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    ....
     
    #18 NJ2018PRIUSC, Mar 17, 2021
    Last edited: Mar 17, 2021
  19. NJ2018PRIUSC

    NJ2018PRIUSC Junior Member

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    So, I’ve learned from several sources that OEM batteries for later mode Prius C are on national backorder. There is no aftermarket replacement.

    The OEM battery:
    2880021211 - Vehicle Battery - Genuine Toyota Part

    is rated:
    20HR 35Ah CCA 240A

    the owners manual states:
    Use a 12-volt battery that the case size is same as the previous one (LN0), 20 hour rate capacity (20HR) is equivalent (35Ah) or greater, and performance rating (CCA) is equivalent (240A) or greater.

    This Toyota document lists H3(LN0):
    https://www.toyotapartsandservice.com/wp-content/uploads/2020/08/03_Batteries2020_hi.pdf

    Assuming that I can find an AGM battery that fits, has compatible terminal diameters and a vent hole on the correct side, how much “greater” can I go for Ah and CCA?

    My every other day voltage tests show the current battery is clearly on the verge of being, if not already, toast.

    Thanks.
     
    #19 NJ2018PRIUSC, Mar 18, 2021
    Last edited: Mar 18, 2021
  20. sam spade 2

    sam spade 2 Senior Member

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    Of course there IS an aftermarket replacement; several probably depending on your mechanical skills and ingenuity in making it "fit".
    There might not be an "exact fit" but it doesn't need to be exact.

    You don't HAVE to have a vent if it is a sealed AGM and the capacity ratings won't be a problem as long as they are close.
    They CAN'T be that much more if the physical size is close.
     
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