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12V Battery Charger Question

Discussion in 'Gen III 2010+ Prius Care, Maintenance and Troubles' started by vinnie97, Jan 1, 2012.

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  1. vinnie97

    vinnie97 Whatever Works

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    I hadn't researched this extensively yet in the case of the Prius, but due to its unique design, is the cigarette outlet a valid place to trickle charge the 12V battery on the Gen III? I was considering a battery like this: Shop Stanley 2-Amp Battery Maintainer and Charger at Lowes.com

    However, it may be required to connect it to the battery terminals themselves, but I just wanted to ask the experts before making any assumptions. I realize this wouldn't be a solution for emergency jumps, so perhaps either a 6-amp or 15-amp charger would be more appropriate for those occasions?
  2. efusco

    efusco Troll Slayer Staff Member

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    You cannot use the 12v power outlet to charge the battery, it is disconnected when the power is off.

    However, you do not need to attach directly to the battery terminals either (the battery is hard to access directly in the back of the car). There are connections for jumping (or charging) under the hood and that is shown in your owner's manual.
    2 people like this.
  3. vinnie97

    vinnie97 Whatever Works

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    'Preciate it, I recall there being some battery access under the hood. I'll consult the manual and forget the 12v power outlet idea. ;)

    PS. What is a sufficient amperage charger for a typical 12v car battery?
  4. andyprius

    andyprius Senior Member

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    Yes you can charge a small battery from the accesory plug, I do it often when I am on a trip. I use a small block, sealed, alarm battery 7AH I wanted to see just how good it was in a emergency, and keep it under the right seat when not in use ( generally the case ) Evan is correct that no 12V is there when the car is OFF, good thing! So your choice, you can leave it connected or remove it. Incidently when the car was new I drove with this battery about 8 miles, connected to under hood terminals with the regular 12V disconnected. :cheer2:
  5. qbee42

    qbee42 My other car is a boat

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    The OP was asking the other way around: they want to charge the 12V battery in the Prius from the accessory jack, not charge a battery *from* the jack. This will not work without modification.

    Tom
  6. andyprius

    andyprius Senior Member

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    Agree, that's a output. ???? I don't see the purpose, the HV is charging the 12V. When the car is off, so is the accesory plug.
  7. vinnie97

    vinnie97 Whatever Works

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    The purpose would be in the event the 12V dies, and I need to recharge it. ;) Andy, are you claiming the hybrid battery actively charges the 12V when the vehicle is off? I don't think you were implying that because I don't believe that's correct...
  8. andyprius

    andyprius Senior Member

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    No, the 12V bat is getting a charge from the HV, at that time 12V is present at the accesory plug. As I said it's a output. And never an input.:D To answer your original question, the 2 anpere from Lowes would probably be OK, I believe the recommended is 3 Amps or less / about once every 6 months.
  9. Willem

    Willem Junior Member

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    I wish I saw that before I dismantled the rear deck to gain access to jump my wife's VW.

    It was in my driveway, but it was dark, windy and drizzling rain. Under those conditions, my (cheap) LED flashlight did not reveal such an option. The only thing I saw was a reference to the 12-volt battery being in the back.

    And getting all the shrouds and associated stuff back to where it was before exposing the battery was not easy.

    Lesson learned: Read the Manual!

    Thanks again, efusco!
  10. richard schumacher

    richard schumacher shortbus driver

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    Whoa, whoa, whoa: you shouldn't be jumping *from* a Prius *to* anything else. The Prius' 12V battery, wiring harness, controller, fuses, and inverter are not up to that task. Doing it the way you did it, directly from the Prius battery, is the least risky way, but you were lucky if the jump worked and everything on the Prius still worked afterwards.
  11. vinnie97

    vinnie97 Whatever Works

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    Right, thanks. I don't let the car sit for extended periods, so I should be okay with getting a more robust charger with a higher amperage (that can top off the battery in 30 minutes as opposed to 30 hours ;)) for emergencies. Would a 6-amp or 15-amp be sufficient for this purpose?
  12. jdenenberg

    jdenenberg EE Professor

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    1 person likes this.
  13. vinnie97

    vinnie97 Whatever Works

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    It looks that it can be 4.2 Amps or under, according to the manual:



    I still wonder if a charger with higher amperage (I bought this one for at-home emergencies: Shop Stanley 6-Amp Automatic Battery Charger with 8-Amp "Quick Start Timer" at Lowes.com) would be suitable in the rare event the battery is unexpectedly drained.
  14. Mendel Leisk

    Mendel Leisk Senior Member

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    I've got a 6 amp "automatic" charger. Haven't been using it much lately, using instead a 1.5 amp CTEK charger, but I recall the 6 amp would show a charging rate around 2 amp when I used it. Due to the automatic feature at work?
  15. vinnie97

    vinnie97 Whatever Works

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    Yes, it sounds to me that feature would prevent any untoward unsafe rapid charging of the battery, and your experience confirms.
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