My Bosch 12V AGM battery was 8 years old in my 2008!

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by JahT, May 10, 2022.

  1. JahT

    JahT Member

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    I didn't bother testing it, I just replaced it with an OEM after trickle charging it to full with a batt. maintainer. There were no obvious problems or codes, but it felt like the HV battery state of charge was acting weird depending on if I had the AC on or not, the keyless entry seemed less responsive even with a new FOB battery, but the lights didn't seem dimmer and it always started fine.

    Would having an older (8 yr) 12V battery affect my Dr. Prius test results? I haven't tested it again yet, but I am hoping maybe I was getting inaccurate results. I know Dr. Prius doesn't test the 12V battery, but if the Hybrid system is having to charge the 12V more, it seems like it may impact the results.

    Any other benefits from a fresh 12V?

    I checked the MFD service menu - display setting to see voltage - both before and after the new battery and the voltage seems similar with the car off, 12.2V at rest, and dips a bit below 11.9 with headlights on. So that may not be a very accurate way to test battery health.

    p.s. maybe one benefit of a cheap battery is that it "dies" more definitively than quality brands?
     
    #1 JahT, May 10, 2022
  2. Mendel Leisk

    Mendel Leisk Senior Member

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    A DIY level 12 volt battery tester is very useful to acquire; they're about $50~80 USD. I'm using an older Clore Solar BA5; I believe BA9 is the current itteration. Ancel's also a respected name.
     
    #2 Mendel Leisk, May 10, 2022
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  3. bisco

    bisco cookie crumbler

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    a serviceable 12v has no detrimental effects. but one that can still start the car, yet requires more charging from the inverter will require more juice from the hybrid battery, and consequently more engine run time, lowering mpg's.
    nothing scientific, but many have reported seeing higher mpg's after replacing an old 12 volt.
     
    #3 bisco, May 10, 2022
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  4. JahT

    JahT Member

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    You are correct, I have been meaning to buy one for a while. Can you load test the battery in the car with everything hooked up to it, or is it best to isolate it?

    I was going to try to test this one just for the knowledge of what state it was in, even if it is still going back as a core. I have a family member who wasn't sure abut hybrids and bought a Matrix when we bought the Prius in 2008 and we have compared our maintenance costs over the years, they also are running on an 8 year battery that the mechanic recently tested and said was "good", not sure what brand it is. Seems both lasted so long being in daily drivers.

    Thank you, the engine idles higher but then I remembered that is likely just the ECU recalibrating. I hope to see some better mpg numbers in the next few weeks.
     
    #4 JahT, May 10, 2022
  5. Mendel Leisk

    Mendel Leisk Senior Member

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    Yes, no problem with the battery being installed. The main issue is the clamps of my tester have to be on the battery posts. I've found in practice if they're slipping off the post, clamping to the cable clamps at the posts usually works ok as well. If for example I were to connect the tester at the under-hood jump point and a ground, it balks, gives an error message of some sort.

    Similarly with charging: our car is used quite infrequently the last few years, what with retirement, covid, changing lifestyle. I'm using a CTEK 4.3 charger, pretty much round-the-clock. Owner's Manual says something about removing battery from car before charging. I've never done that. In the last few years I've used the charger's quick-connect gizmo, permanently installed: so no fussing with alligator clips. Pos lead of that gizmo is connected where 12 volts comes into the under-hood fuse box, and neg lead I found an unused threaded hole nearby, connected with a spare metric bolt I had.
     
    #5 Mendel Leisk, May 11, 2022
    Last edited: May 11, 2022
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