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Batteries, Jump Starting, Ready Light?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by drum365, Aug 19, 2022.

  1. drum365

    drum365 New Member

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    I hope you all will forgive me for a one-and-done post. My brother has been in a long-term care facility, and I thought it would be a good idea to start his 2008 Prius since it has been sitting for a long time. It was stone-cold dead. No door locks, no dash lights, nothing.

    I was able to jumpstart the battery and drive it, but I'm very confused and hope you all can help. Please excuse me if some of these are "dumb" questions. I have zero experience with hybrids.

    First dumb question: does the car have two batteries, one for driving the wheels and a 12V battery for starting, etc.? The 12V can discharge without draining the "main" battery?

    I'd drive a regular internal combustion car for 20 minutes or so to recharge the battery. Will that recharge the 12V in the Prius, too?

    When I started the Prius, the info window showed four blue bars on the info screen. Coasting down my brother's hill got it up to one green bar, but then driving in stop-and-go traffic with the AC on, I got all the way down to 2 or 3 blue bars. I got scared and turned off the AC. (Is it correct to assume the internal combustion motor would keep me going even if the main battery showed zero bars?)

    I read something that gave me the impression that pushing the Power button - so "Ready" lights up on the dashboard - causes the main battery to start the 12V battery. Is this right? If I just left the car sitting in Ready mode, would the 12V battery eventually be charged?

    Again - sorry for all the dumb questions. Thanks in advance for any help!
     
    #1 drum365, Aug 19, 2022
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  2. JC91006

    JC91006 Senior Member

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    The battery probably has become weak and out of balance. Older hybrids will have this problem and the car's battery will eventually fail and you'll need to get a new one.

    The 12v battery is just to start the computers, after that, the hybrid battery takes over. They are separate units and have really no relation
     
    #2 JC91006, Aug 20, 2022
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  3. dolj

    dolj Senior Member

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    Hi and welcome to PriusChat.
    Yes, exactly it has two batteries. They are not connected and so the 12 V is quite capable of discharging without draining the main battery which is called the hybrid vehicle (HV) battery.
    I doubt even in a regular car driving for only 20 mins would charge a flat battery, but more so in this particular model of hybrid. It will charge once in READY but will take more like 11 - 18 hours to fully charge a totally flat battery. So, it is better to put the battery on charge using a multi-stage fully automatic 4 Amp battery charger and leave it on until the charger says it is done. The advantage of this type of charger you can just leave it on the battery ad infinitum and it will keep the battery fully cahrged. This would be a perfect solution to the scenario you have with this car where it is not being driven regularly.
    This is normal behavior, don't worry about it. While you're in the stop/go traffic the engine will start periodically to keep the HV battery at 2-3 bars and then as soon as you're out of the stop/go traffic and cruising again it will charge the HV battery up to where it likes it at around 5-6 bars.
    Not sure what you mean by "causes the main battery start the 12 V battery" but yes, the HV battery will start to charge the 12 V as mentioned above. If you leave it for around 11 to 18 hours you should have a full 12 V again.
    The only dumb questions are the ones not asked, so don't sweat it.
     
    #3 dolj, Aug 20, 2022
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  4. drum365

    drum365 New Member

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    Three Touring
    Wow - thanks JC91006 and dolj for the detailed (and patient) answers. And dolj - sorry for the brainfart. I meant "charge the 12v battery" not "start the 12V battery." I'll try leaving the car in Ready mode for now, let it charge overnight and see what happens. I've got a smart charger at home in Sacramento and the next time I come down to LA in a few weeks, I'll bring it and a long extension cord and try to get a good charge on it.

    Thanks once again - I really appreciate it.
     
    #4 drum365, Aug 20, 2022
  5. bisco

    bisco cookie crumbler

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    you may find that the 12v will not hold a charge, no matter how long or what type of charger.
    in that case, you will have to replace it.

    if by any chance your brother will not need it again (i hope not) now is an excellent time to sell, as used prius prices have never been higher, especially in socal.
     
    #5 bisco, Aug 20, 2022
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