Low 12-volt battery - questions about recharging

Discussion in 'Gen 4 Prius Care, Maintenance and Troubleshooting' started by kortheo, Mar 27, 2023.

  1. kortheo

    kortheo Junior Member

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    Hello,

    I've read a few threads on this topic, but I wanted to ask in my own thread because there are a couple details I'm still not clear on.

    I've got a 2017 Prius. Got back from vacation and got the "Low 12-Volt battery / Apply parking brake securely while parking / see owner's manual" message. I just bought a plug-in battery charger (Noco Genius 10) and I'm going go try to recharge it, but this is my first time doing this.

    Questions:

    1. The 12V battery is about 2 years old. It was put in by the dealer, part number 00544H4052470. This is the first time it's been low. I'm realizing that driving our car 1-2 times per week for less than 30 minutes each way is probably the cause of this battery draining. I'll try to drive it for at least one longer drive per week to give it a chance to charge up, or start using a battery maintainer. Based on this, do you agree that it's probably just our usage of the car causing it to be low rather than the battery being bad? Should I have the dealer inspect the battery?

    2. The Prius User's Manual states:

    "If recharging with the 12-volt battery installed on the vehicle, be sure to disconnect the ground cable"

    Forgive my ignorance, but what is the ground cable and how do I disconnect it? Is that just the cable coming off of the negative battery terminal? I saw some posters in another thread on this topic saying this step was unnecessary. Do I need to disconnect the cable in this scenario, i.e. using a plug-charger to charge the battery for a few hours? If I don't, what is the risk?

    I appreciate any advise, thanks.

    Travis
     
  2. FuelMiser

    FuelMiser Senior Member

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    The battery is probably degraded (ability to hold a charge) from new, but there is a lot of room between degraded and bad. You can have it tested* to see how much capacity is left, but I would try an Auto Parts store before a dealer since the dealer is probably hard-wired to tell you to replace the battery.

    *I purchased my own TOPDON BT100 battery tester from Amazon

    I am still on my original battery in my 2016, and it has gone flat several times. The first time it did, I connected a charger overnight without disconnecting the negative terminal, and DID NOT get a good charge--the car still would not start. So, I then disconnected the negative cable and connected the battery charger directly to the negative post, and this resulted in a good charge. But since then, I purchased the NOCO GB40 jump starter and this provides an immediate jump start in seconds rather than needing to wait for a re-charge. I figured this is preferred, especially if the battery goes flat when away from home. I now keep the NOCO in the car in case I need it anywhere.

    Screenshot 2023-03-27 at 6.34.40 PM.png
     
  3. Doug McC

    Doug McC Active Member

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    If the battery is less than two years old it may be covered by a 100% replacement since it was installed by the dealer. Even after that two year period there is a prorated period that pays a significant amount and the dealership has to prove the battery has failed a specific test in order to meet the warranty requirements. So I doubt they will push a replacement if the battery isn’t bad.
    The Topdon 100 is an excellent battery tester as it displays the Internal Resistance of the battery not just a good or bad rating. Using it is more convenient than heading to a parts store for a quick test.
    You’re driving the vehicle enough to charge the battery, assuming you are not running excessive loads when it is not in Ready or Ignition mode. Or leaving your doors and hatch open with the car off.
    If you decide to charge it yourself, head the limit on the maximum amperage, using a trickle charger, making sure your connections to the battery are secure, and you won’t need to disconnect the cable. If you use a higher charge rate than recommended, then you definitely want to disconnect the cables to protect the vehicle’s electronics.
     
  4. Mendel Leisk

    Mendel Leisk Patron saint of newly poured sidewalks

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    I NEVER do this, and our 2010 pretty much lives on a charger; currently car gets driven about once a week.

    Page 599 of Owner's Manual recommends 5 amperage max for charging. The charger you got is double that. Not sure how critical that is, but food for thought. Exchange for something with more suitable amperage, if possible?
     
    #4 Mendel Leisk, Mar 28, 2023
    Last edited: Mar 28, 2023
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  5. bisco

    bisco cookie crumbler

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    battery is probably fine

    you aren't driving enough

    no need to disconnect anything, just put the clips on and plug it in
     
  6. kortheo

    kortheo Junior Member

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    Wow thanks for pointing that out. I actually thought I saw that mentioned somewhere and was going to double check it before I charged. The owners manual says "The battery may explode if charged at a quicker rate" lol. So I'm very glad I didn't just go for it. I'll exchange it for the 5A version.

    And thanks for confirming about the cable! I think that's everything I need to know (for now) :)
     
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  7. kortheo

    kortheo Junior Member

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    Also I just realized that I should probably buy a portable jump starter, rather than a battery charger, in my scenario. So something like this instead:

     
  8. Mendel Leisk

    Mendel Leisk Patron saint of newly poured sidewalks

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    Jump starters for emergency starts, when the battery's dead. But for maintaining a battery, restoring it when it's been drained, a good smart charger is what you need.
     
  9. bisco

    bisco cookie crumbler

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