Replace OEM 12V battery with Group 25 AGM

Discussion in 'Gen 3 Prius Accessories and Modifications' started by cproaudio, Jul 9, 2015.

  1. sam spade 2

    sam spade 2 Senior Member

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    That's because it is actually SEALED up to some preset "pop off" pressure which should never be reached in normal use.
    The vent tube is overkill.

    THEN.....the electronics that Harbor Freight sells is cheap Chinese JUNK.
    I would never buy any of it, except for the little red multi-meter for $7 that seems to work quite good.
    That includes batteries.
    Especially one of lower capacity than the original.

    Overall a VERY bad plan, in my opinion.
     
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  2. C Wagner

    C Wagner Junior Member

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    Actually, the little red HF multimeter isn't that good - I only found this out when doing the hybrid HV battery rebuild and balance. It's off vs a couple of more expensive meters I checked it with by xx tenths of a volt. It didn't matter once I knew that, but it was important to know for the max discharge and charge voltage points. As it happened the module charger itself was off too!
     
  3. sam spade 2

    sam spade 2 Senior Member

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    I'm sure that their "quality control" isn't that good overall but...........
    I'm on about my tenth one now and haven't found that problem with any of them.
    I presently have: one at home. One in each car. One in my Spyder. One in my fishing cabin and one on the boat.
    But I seldom use it for anything except checking the "automotive" batteries and flashlight cells.

    At $7 each, the 6 I presently have cost me about $42. Less than one "good" meter.......and I don't have the problem of needing a meter at one place and having it BE at another.
     
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  4. C Wagner

    C Wagner Junior Member

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    I think all of those HF meters were free when I got them, with coupon. Alas, now they are charging for them...
     
  5. Grit

    Grit Senior Member

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    id love to see that under many cycles with engine always off does to the life span of the 12v bat.
     
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  6. black_jmyntrn

    black_jmyntrn Junior Member

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  7. C Wagner

    C Wagner Junior Member

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    Yes, it will be interesting to see. I note that the OEM battery for non-SKS is 35AH also, so this kludge is not so much an under powered kludge as a size/post one. I ordered U1-SAE adapters from ebay and a special JIS to SAE adapter for the car-side connector (why did Toyota use JIS on US priuses and SAE on Japanese priuses, as I've been told???) The major impediment to my new battery from Harbor Freight is that they are holding back the 20% coupons these days, it's cold outside in Boston and the old OEM 2012 battery is holding at about 11.8 in these March temps!
     
  8. Joele3

    Joele3 Active Member

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    Fits like a glove. Going on 7 years on OEM battery. I'm running two amplifiers, wanted to throw in a larger battery. Thanks for the info on this thread. I ordered the adapters on ebay. I noticed sometimes my car wouldn't shut off. ICE would always stay idling until I would turn off the car. I read on another thread replacing the battery fixed it. So far I haven't noticed it doing the same thing. Up next is new struts or coils. So hard to find parts in stock for the V.
     

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  9. black_jmyntrn

    black_jmyntrn Junior Member

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    I'm working with a few vendors, they have springs for the V, not lowering but heavy duty ones that can provide lift if you want.
     
  10. C Wagner

    C Wagner Junior Member

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    I wanted to update those lurking and the future thread readers, that I did go buy a 35AH AGM battery and have installed it - and after a couple of days and some cornering, it's still great.

    I'd read here that a 35AH AGM SLA (unvented though) would be fine. I noted that the non-SKS cars used a battery of about the same size. I resolved to turn off SKS if I go away on long vacations. I also noted that some have said the official 45AH OEM battery costs about $250 (you install) at my dealer and the 35AH battery was sometimes available at about 1/4 that price, so even if the battery lasted not so long, due to SKS drain it a few too many times, it would probably be worth trying.

    I waited desperately for a Harbor Freight coupon and planned to buy a battery that used to be a better price but is now $75. No 20% - after waiting a long time, ... I bought a Mighty Max from Ebay for about $60 delivered. It seems good.

    A conversion was needed. I had to seek out a priuschat aficionado who sold me a small part that changes the car's terminal clamps from JIS to SAE (US standard). $20 I also needed tab to post adapters. Those were $10 on Ebay for U1 to SAE. Don't overtighten, or your tabs will rotate! Anyway, after those modifications, the new little battery went in to the place where the big battery was before. It was shimmed so it doesn't slosh around and will stay clamped down.

    The immediate thing I noticed, vs an 8 year old OEM battery that couldn't really hold a charge, is that it seemed MPG is 2-3 higher. My test wasn't scientific, but might be even better as I had been driving mostly without A/C or heat and without headlights during day. On the day I drove the car 200 miles, mostly highway, on a stretch I'd driven a few weeks ago with the old battery, I used the A/C, heat and headlights most of the time -- and got the 2-3 mpg higher.

    I may work on figuring out where to drill a hole in the Mighty Max battery to attach the car's vent pipe, but I'll probably do this after the MM battery warranty is over...
     
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