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ONE GOOD WAY TO KEEP 12V BATTERY CHARGED UP

Discussion in 'Prime Care, Maintenance and Troubleshooting' started by srivenkat, Jan 18, 2021.

  1. sam spade 2

    sam spade 2 Senior Member

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    Actually the method you propose is not a really GOOD way to keep the battery charged either.

    Driving the car has more advantages.......but that has been covered in other threads too.

    I think this thread really accomplishes nothing useful.
    Sorry.
     
    Mendel Leisk likes this.
  2. Mendel Leisk

    Mendel Leisk Senior Member

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    I seem to recall protracted idling can actually run the 12 volt DOWN (excuse cap lock, highlighting is a pain on phone). Maybe more so on conventional car.. And, idling a Prius is an exercise in futility, it’ll maybe shut down in 2~3 min. If a dedicated charger takes at least 3~4 hours, what does 5 minutes idling do...
     
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  3. ChapmanF

    ChapmanF Senior Member

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    The engine. 12 volt battery keeps charging though, as long as the READY light's on. Doesn't matter if the engine's running.
     
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  4. srivenkat

    srivenkat Active Member

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    If a Prime is being regularly driven so infrequently and for short distances, the ideal thing to do would be placing the 12V on a battery tender like Mendel suggests. The OP suggestion in this thread is for the once in a great while special circumstance where the 12V might be getting too low because of temporary changes in driving routines.
     
    #24 srivenkat, Jan 21, 2021
    Last edited: Jan 21, 2021
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  5. AldoON

    AldoON Member

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    I'm finding this thread useful since I don't have a convenient place to plug anything in at home.

    Unless it's a last resort I won't be leaving the car in ready at home. What I may do is leave the car in ready mode while I'm waiting or between errands such as curbside pickup. Typically I used to turn the car off when "idling." Habit from ICE only cars I guess.
     
  6. pghyndman

    pghyndman Active Member

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    Ooops... Disregard!
     
  7. srivenkat

    srivenkat Active Member

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    Yes, you could leave it in READY mode in between errands, but you would have to lock the doors using the metal key from the outside, if you are concerned about safety or some thug could drive it away, even when the keyfob might be with you.
     
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  8. ChapmanF

    ChapmanF Senior Member

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    If you stay in the car beween errands or while waiting for curbside delivery, then you only worry about the thugs who would drive off with you in it.
     
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  9. srivenkat

    srivenkat Active Member

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    That would only be a concern if you are beautiful or rich (or both) :D
     
  10. Maggy Field

    Maggy Field Junior Member

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    I believe this is one of the more important posts on this thread. It points out how difficult it can be for even well informed people to really grok the entirely different purpose of the 12V battery in the Prius/Prime. Of course precautions are necessary to prevent excessive discharging, but as said, if it starts the computer it has enough charge.

    I was following with interest another thread about low voltage on the accessory port while driving. I haven't done my testing under load yet, but here is a graph of the voltage directly on the 12 Volt battery terminals beginning after an overnight charge just before I took the car for an EV drive that never required the ICE to start. The X axis is seconds with measurements made every 2 seconds. It covers roughly 2 hours of running errands with the time I was parked evident as flat areas of no activity. Before READY the voltage was at about 12.45 volts. The voltage varies from about 14.3 to short spikes as low as 11.6 VDC during the drive. When I parked it had apparently charged to about 12.6 volts.

    So I hope you find it interesting. I will do this again with a substantial, 60 watt or so, load on the accessory port and will post that data on the other thread about low accessory port voltage.
    Prime 12VDC Voltage.PNG
     
    #30 Maggy Field, Apr 9, 2021
    Last edited: Apr 9, 2021
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  11. bisco

    bisco cookie crumbler

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    'if it starts the computer, it has enough charge'

    this is no way to measure battery health
     
  12. Maggy Field

    Maggy Field Junior Member

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    True, that would require a load test, but that was not the point. The point was to relax and not obsess over the exact voltage. The battery can be perfectly healthy if the system has chosen to leave it a couple of tenths of a volt lower or higher. As long as it will start the computer it is functioning properly within the system. It's overall health is another issue.
     
    #32 Maggy Field, Apr 9, 2021
    Last edited: Apr 9, 2021