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DIY report: replace 12v battery with 55ah "ExpertPower" from Ebay

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Questolicious, Mar 7, 2022.

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  1. Questolicious

    Questolicious New Member

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    Successful report of replacing the 12v battery on a 2005 Prius with an aftermarket battery from Ebay.

    There's a lot of info about different ways to do this in the forums, but no comprehensive tutorial that I could find, so I thought this might be useful to write up.


    Battery:

    ExpertPower 12v 55ah AGM battery (with internally threaded terminals)
    $120 on Ebay from seller "expertbattery"
    12 Volt (12V) 55 Amp (55Ah) VRLA AGM Sealed Lead Acid Battery 55 AMPS HIGH CAP | eBay

    Note that the photo in the listing has no brand name, while the battery that actually arrived is branded "ExpertPower." Also it says "Non-Spillable Lead Acid Battery" instead of AGM, but my understanding is that these are the same.

    This battery was chosen after reading a post by Britprius. Not only is the ExpertPower battery much cheaper than OEM, it's also higher capacity (55ah instead of 45ah) and thus better at handling long slow discharges (although I'm not sure if the battery I got is actually a mobility battery or not). None of the other brand recommendations from previous threads, such as Bosch, were available. The MightyMax battery came up a lot in searches, but the flag terminals seemed more difficult to deal with than internally threaded ones.

    Britprius's excellent post:
    Fitting mobility 12volt AGM battery. | PriusChat

    Also thanks to PriusCamper's recommendations for terminal modifications in this post:
    Replace 2005 12 Volt Battery | PriusChat


    Other parts:

    M6 bolt, 1.00 pitch, 25mm length, hex head, x2
    M6 washer, medium size, x4
    M6 washer, large size, x1
    M6 nut (reused from positive terminal of old battery)
    M6 bolt, 1.00 pitch, 35mm length, hex head with washer, x1


    Result:

    Works great! Plus I instantly gained an extra 2-5 mpg, nice bonus :)


    Instructions:

    1. Make sure car is off. Remove trunk lining and black plastic crate underneath. Remove side trim. Now you should have full access to the 12v battery.

    2. Remove the brake control power supply (the black box in front of the battery). Unplug all connectors. Remove big vent tube on the left. Remove the black plastic piece on top of the battery where the connectors plugged in. Disconnect both terminals (recommend negative first, then positive, to prevent the chance of a short circuit with a metal tool). Remove old 12v battery.

    [​IMG]

    [​IMG]


    Old battery and new battery side by side. The new one is slightly taller and slightly wider.

    [​IMG]


    Test fitting: new battery goes into the bottom bracket just fine, despite being bigger.

    [​IMG]


    3. Transfer the negative terminal lead from the old battery to the new one. As PriusCamper suggests, I used two M6 washers to sandwich the lead and then an M6 bolt to screw into the battery.

    [​IMG]

    [​IMG]


    It may also be possible (I realized later) to turn the negative lead on its side and screw it in directly, without the need for extra washers, as shown in Britprius's post:

    [​IMG]

    4. Attach the top bracket. This is the part that took the longest to figure out. In the end all I did was use a longer screw.

    Illustration of the problem:

    [​IMG]

    Since the new battery is taller, the top bracket no longer fits. PriusCamper suggests using a vise clamp (presumably with a hammer) to rebend it. However, I found the rebending process was not ideal. The metal kept twisting so it wasn't square anymore, it looked ugly, and not everyone has a vise clamp at home. And in the end, the rebent bracket still wasn't long enough, so I bent it back to the original shape and went for plan B: just use a longer bolt.

    With the M6 35mm bolt in place, the bracket is held tight and there is no wiggle room:

    [​IMG]

    [​IMG]


    5. Drill a new hole and attach the black plastic piece (where the harness connectors used to be) to the top metal bracket. It attaches with a small plastic clip, but because the new battery is bigger, the original placement is not quite right anymore. To make it align correctly with the positive terminal, I drilled a new hole using a 3/16" drill bit.

    [​IMG]


    6. Attach the positive terminal lead to the battery. I used the same strategy as before, with two M6 washers sandwiching the lead, but with the addition of an extra-large washer on top (because the smaller washer kept slipping) and an M6 nut on the bottom (to make the heights line up correctly). The M6 nut was taken from this same positive terminal lead, since its corresponding bolt was no longer needed.

    [​IMG]

    [​IMG]

    It may also be possible (I realized later) to combine steps 5 and 6 here by getting rid of the leftmost stack of bolts/washers completely and instead bolting directly like this, as shown in Britprius's post:

    [​IMG]

    All set with the new battery:

    [​IMG]


    7. Time to reconnect all the things. But first, check the orientation of the negative terminal lead (the picture below is correct) to ensure it will screw into the wall properly. Mine was pointing the wrong way, so I had to take out the brake control power supply an extra time to fix it, no biggie.

    Reattach big vent tube. Reattach brake control power supply. Plug in all harness connectors. Reattach negative terminal to the chassis.

    [​IMG]


    8. Trim about 3/8" off the legs of the trunk side trim piece, since the battery is now a bit taller. Only 2 of the 3 legs need trimming. Reinstall all trunk trim.

    [​IMG]


    9. Turn on the car. It works! I'm so happy with my new improved mpg too :)
     
    #1 Questolicious, Mar 7, 2022
    Last edited: Mar 7, 2022
  2. PriusCamper

    PriusCamper Senior Member

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    Wow! This is an awesome post! So grateful you mentioned Britprius as its source of origin too! I support everything you're saying in this one!

    PS: Photos are not visible. Maybe try to repost them?
     
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  3. Questolicious

    Questolicious New Member

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    Thanks!!!

    Yeah, I'm working on redoing the photos, they showed up fine in the editor but not on post. Obviously not the original thread topic, but if someone could clarify whether this forum supports external file linking, that would be great. Photobucket seems to work, but not PostImage...?

    Edit: Go to https://priuschat.com/media/add. Create a new album and upload photos. Right click on each photo to get the image URL. Then in the editing window, click on the button that looks like a mountain and sun, and paste the URL. Now all the links are internal.
     
    #3 Questolicious, Mar 7, 2022
    Last edited: Mar 7, 2022
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  4. PriusCamper

    PriusCamper Senior Member

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    upload photos direct is best...
     
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  5. TMR-JWAP

    TMR-JWAP Senior Member

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    The metal kept twisting so it wasn't square anymore, it looked ugly,

    You're worried about that metal plate being ugly, but nothing else?

    They make JIC sized terminals with a threaded stud that screw into those "internally threaded" terminals. That way you can keep your OEM battery fasteners and not crush everything out of shape.
     
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  6. Another

    Another Senior Member

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    Seems like a lot of work just to avoid buying an OEM battery. What’s the point?
     
  7. Questolicious

    Questolicious New Member

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    Do you have a link for these? I looked but couldn't find any.
     
  8. PriusCamper

    PriusCamper Senior Member

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    The point is they have more amp-hours than garbage OEM and they also cost near 1/3rd the price...
     
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  9. PriusCamper

    PriusCamper Senior Member

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    I've never had to remove the black box next to battery to get that bolt to fit, nor have I ever had to cut the plastic posts. Also not sure about the bolt on the bottom of the terminal? I just use a flat washer in that spot.
     
  10. Another

    Another Senior Member

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  11. PriusCamper

    PriusCamper Senior Member

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    Lol, another clueless Nielson article that's poorly researched. The reason the price is higher is because they're different and unique in the automotive sector, so you can get away with inflating the price...

    However in the back up computer power supply and mobility battery sector AGM are standard and not unique at all, which means the prices are way more competitive and you can find a lower price and higher quality of amp-hours compared to the price gouging opportunists in the automotive sector.
     
  12. TMR-JWAP

    TMR-JWAP Senior Member

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    The TrueStart in my 2005 was manufactured in 2011. Rated for 325 cca. Tested it yesterday when my son brought the car over to the house to swap cars with my 2006. (gonna put 2005 up for sale soon) It tested at 350 on my electronic load tester. The 2006 has a TrueStart manufactured in 2013 and tested at 300. There may be better and/or less expensive batteries, but I wouldn't go as far as saying the TrueStarts are garbage :)
     
  13. PriusCamper

    PriusCamper Senior Member

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    Agreed, my hyperbole infection has been flaring up lately. :) When all your car battery has to do is turn on some computers and some relays, just about anything can work... Longevity on the other hand, that's a different story.
     
  14. TMR-JWAP

    TMR-JWAP Senior Member

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    Odyssey JIS Battery Terminals - JHPUSA

    These are probably a bit more expensive than a lead version. Assuming the threads are the same. They may offer additional versions.

    Amazon.com: AUTUT 2 Pairs Car Auto Positive Negative Battery Post Terminal Adapter Converter, 3/8-Inch Thread : Automotive

    These are for SAE size terminals. Cheap, but wrong size. Could be cut down? Maybe I'll order a couple packs and throw them on my mini-lathe to make then JIS size. I'm sure someone could use them if the JIS is not available in lead. The threads on your new battery are M6? Are all the mobility batteries M6 or can they be had with 3/8?

    Hacksaw off the terminals of the old battery, poke a hole down the center with a M6 bit and use the bolt to lock it in place.

    Put an M6 stud in the hole until it's bottomed out with about an inch sticking up. Drill and tap the (hacksawed) terminal to m6x1(?) thread size and screw it down on there.

    All kinds of option, lol.
     
    #14 TMR-JWAP, Mar 7, 2022
    Last edited: Mar 7, 2022
  15. ChapmanF

    ChapmanF Senior Member

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    I've replaced a couple OEM Prius aux batteries, both at around the tenth year. That's good enough longevity to satisfy me.
     
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  16. Questolicious

    Questolicious New Member

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    Agreed! I just like the price point better ($120 vs. $230 for OEM) for a car I'll probably only have for a few years. Plus the capacity is bigger (55ah vs. 45ah), so less likely to die if I leave the dome light on for a long time. Better AND cheaper seems like a win-win to me.

    (If you have a Gen 3 you'd like to sell, drop me a message...)
     
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  17. TMR-JWAP

    TMR-JWAP Senior Member

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    To each, their own, and we all do what we have to do. I have no issue with that at all.

    With that being said, if I were looking at buying a car and I saw that when I inspected the battery (because I usually do) I would want at least 500 off the price because if an owner has done that to save a few bucks, there's no telling what other sketchy things I could run into.

    The threaded terminals could have SAE terms installed. Then replace the JIS sized clamp at the + term that you took off the fusible link assembly with a full size SAE clamp. Last time I looked, they're available from TOYO for about $10 or a salvage yard for a dollar. Then just get a ground wire that has a SAE clamp. There's yards full of toyotas that have them. I have both of these on the shelf from Camry hybrids just in case I wanted to ever go a similar route. The Camy used full size terminals on the batteries.

    Toyota 90982-05054 is the part number for the (+) terminal clamp.
     
    #17 TMR-JWAP, Mar 7, 2022
    Last edited: Mar 7, 2022
  18. tangerino

    tangerino Junior Member

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    Appreciate the detailed guide, @Questolicious! I just followed it to install mine and was able to combine steps #5-6 by just bolting the positive terminal directly. It was a bit slanted but stacking a few extra washers helped and the connection seems secure.
     
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  19. GaryInSanDiego

    GaryInSanDiego Junior Member

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    Thank you for this great post! This battery has a very small vent hole on the upper side of the battery near the positive terminal. I want to vent this battery, like the OEM battery is vented. To do this, I drilled a 5/16" hole on the top of the lid, about 3/4" from tiny vent hole. I sealed the tiny vent hole with glue, and attached 4 layers of clear packing tape to the top lid to help ensure gases do not leak out from the lid. I then inserted a longer vacuum hose with a 5/16" outside diameter and a 4mm inside diameter. Be very careful when drilling the 5/16" hole in the top of the lid. When I did this, the drill grabbed the plastic top, and drilled down about 1 1/2" accidentally. I'm not sure I hurt anything, because there seems to be a deep cavity there. This design will allow the gases from the battery to vent out of the battery compartment.

    hole drilled in top.jpg

    Here is the battery installed (along with the vent tube).

    vent hose on 12v battery.jpg
     
  20. PriusCamper

    PriusCamper Senior Member

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    I guess you didn't need the battery warranty you gave up by drilling a hole in your battery? Sure would be a bummer if your unnecessary hole damaged the battery. And as we've been arguing for over a decade on here. There's still no proof that this vent will ever be needed. As in VW has been putting the 12v battery inside the car's cabin since the 1930's without venting and without issue.
     
    #20 PriusCamper, Oct 20, 2023
    Last edited: Oct 20, 2023