1. Attachments are working again! Check out this thread for more details and to report any other bugs.

How to check, charge, and where to source the 12v battery

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by rayluo, Dec 23, 2022.

  1. rayluo

    rayluo Junior Member

    Joined:
    Jun 20, 2022
    13
    2
    0
    Location:
    Washington, USA
    Vehicle:
    2007 Prius
    Model:
    N/A
    My Prius needed jump start, twice, during last couple cold winter weeks. When it failed to start, even the dashboard completely went dark. These symptoms all pointed to a weak 12v battery. Here comes my journey, and I hope it will be useful for this community.

    How to charge your 12v battery?

    • If you can jump start your Prius and drive it around for i-dont-know-how-long, it should self-charge. But it is a guesswork. Short trips will not be sufficient, because each starting would consume more than the subsequent short trip can charge back.
    • You can use a lead-acid battery charger (some inexpensive hobby chargers will do) to decisively charge your 12v battery to all-it-can-absorb. The way I do it, I did not bother taking the battery out. I figure I could wire the charger to the jump start terminals under the hood (as that is the safe way to do jump start anyway), yet I chose to wire my charger directly to the 12v battery in the back trunk, while disconnecting its ground cable from the chassis, this way I am still confident that the charging will not fry my Prius electronics.

    How to check whether the 12v battery is approaching end of life?

    • Some auto parts store will provide free battery load test. Not sure how long they are supposed to "load test" it, but a technician in Toyota dealership used a handheld device and it gave a "needs replacement" result within minutes.
    • You could use a multimeter to check its voltage. But, as it turns out, Prius has a built-in voltage check. Just shut down your Prius, then press the start button once to turn on the dashboard. Press and hold the DISPLAY button, and quickly flip the headlight on and off 3 times. Now your Prius monitor will show a diagnose menu. Go into "Menu", "Display Check", "Vehicle Check". And then you will see the voltage of your 12v battery. It is expected to remain around 12v (duh) when your engine is not running. For a depleted battery, it would likely be around 11v, and even dip down to 10v (which is likely insufficient to start your engine) or even sub-10v (which will not even be enough to light up your dashboard).
    • If you went with the hobby charger route to charge it, some hobby charger will give you a stat on how many Ah were charged into the 12v battery. My failing 6-year-old 12v battery can store only 2Ah, which was merely enough to crank up my engine several times. A healthy 12v battery will possibly hold 12~24Ah.

    Where to source a replacement 12v battery?

    Prius (at least its 2nd gen) does not use regular 12v battery. You need to find battery with "size S46B24R". You should shop around to find the best deal. As of this writing,
    • My local O'Reilly Auto Parts lists several options, all with 3 year warranty, ranging from $239 to $289.
    • My local Toyota dealership offers Toyota OEM TrueStart battery, with much better 7 year (prorated) warranty, for only $216. The price is (perhaps surprisingly?) cheaper than 3rd-party shops above, but unless you can install it yourself, Toyota Service will also (perhaps understandably?) try to sell you a $199 installation, plus another $1500+ for your approaching scheduled maintenance.
    • And then while I'm writing this post, I stumbled upon this info, that the battery is listed at only $158 per Toyota official website, even potentially "Includes Towing and Installation Labor (Ask your dealer for specific details.)" Data source: Go search "TrueStart Battery Part Number: 0054427060675" in official parts @ toyota @ com /p/TrueStart-Battery/69278353/0054427060675.html (sorry, I am not yet allowed to paste a real link in this forum).

    So, now you have it, this issue can be solved by $158 plus some up to 30-to-60 minutes work.

    Long live our Prius!

    Regards,
    Ray
     
  2. rayluo

    rayluo Junior Member

    Joined:
    Jun 20, 2022
    13
    2
    0
    Location:
    Washington, USA
    Vehicle:
    2007 Prius
    Model:
    N/A
    Now I am able to leave a real link here:
    0054427060675 - TrueStart Battery - Genuine Toyota Part


    Also, after you procured your new 12v battery, you can follow this official repair manual to replace the 12v battery: https://attachments.priuschat.com/attachment-files/2017/09/131800_19_-_Starting___Charging.pdf
     
  3. rayluo

    rayluo Junior Member

    Joined:
    Jun 20, 2022
    13
    2
    0
    Location:
    Washington, USA
    Vehicle:
    2007 Prius
    Model:
    N/A
    Some starter battery will provide a Reserve Capacity (RC) rating in their specs. Here comes one more piece of info for the geeks on how to convert the starter battery's RC (Reserve Capacity) rating to Ah (Amp Hours) so that we can compare it with the hobby charger's Ah counter.

    SAE (Society of Automotive Engineers) specifies the capacity of a starter battery by Reserve Capacity (RC). RC reflects the runtime in minutes at a steady discharge of 25A. So, I'll calculate Ah = 25*RC/60. For example, a starter battery with RC=30 will roughly have 12.5Ah capacity.

    Don't worry too much if your years-old starter battery's Ah is lower than its original capacity. Some said it would still be sufficient when it is down to 30% of its original capacity. Perhaps you can consider turning off the keyless entry feature of Prius so that it would presumably consume less electricity while parking in your parking lot overnight.
     
  4. TMR-JWAP

    TMR-JWAP Senior Member

    Joined:
    Aug 12, 2016
    6,058
    5,783
    0
    Location:
    Columbia, SC
    Vehicle:
    2007 Prius
    Model:
    Touring
    #4 TMR-JWAP, Dec 24, 2022
    Last edited: Dec 24, 2022
  5. rayluo

    rayluo Junior Member

    Joined:
    Jun 20, 2022
    13
    2
    0
    Location:
    Washington, USA
    Vehicle:
    2007 Prius
    Model:
    N/A
    Thank you TMR, you made a good point! I was misled by the Toyota website, which does NOT display a red warning message of "this battery will not fit your car" even after I specify my vehicle as Prius 2007. Now I know that they only display a green "this fits your Prius 2007" when browsing the S46B24R or S34B20R. (P.S.: I bought my S46B24R battery over the counter from my local dealership for the same $215 price.)

    So, yeah, the proper 12v battery for a gen 2 Prius with SKS is a 46ah battery.

    Assuming both 46ah and 34ah would fit a gen 2 Prius regardless whether it is equipped with SKS, I would recommend to always pay the extra 10% ($20) to go with the 35% larger capacity 46ah battery so that you will have much larger room for error in case you accidentally leave your headlights on.

    P.S.: Why does this forum not allow me to edit my own old post to change that wrong link error inline?
     
    #5 rayluo, Dec 26, 2022
    Last edited: Dec 26, 2022
  6. dolj

    dolj Senior Member

    Joined:
    May 14, 2012
    7,448
    3,751
    0
    Location:
    Wellington, New Zealand
    Vehicle:
    2007 Prius
    Model:
    N/A
    It's a long story. You have 20-24(??) hours to edit a post before they get frozen for time immemorial.

    If, after that, you see something that you need to change you can enlist the assistance of a moderator and request the change you need to be made. You do this by clicking the Report Button.jpg button at the bottom left of the post.
     
    #6 dolj, Dec 26, 2022
    Last edited: Dec 26, 2022
    Mendel Leisk and rayluo like this.
  7. TMR-JWAP

    TMR-JWAP Senior Member

    Joined:
    Aug 12, 2016
    6,058
    5,783
    0
    Location:
    Columbia, SC
    Vehicle:
    2007 Prius
    Model:
    Touring
    The 46 and 34 ah batteries have different sized battery hold down trays in the trunk. I'm pretty sure a 46ah battery can fit in the 34ah tray, but it's very tight and pushes the end of the battery right up against the rear sheet metal.

    I think the 34 tray can be redrilled for the 46 mounting location/bolts to move it a bit. Otherwise the 46 tray can be purchased from toyo for like $30 or so.
     
  8. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    54,480
    38,106
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Not sure how advantageous it is, but for what it’s worth, instead of “inexpensive hobby charger” I’ve gone with “expensive multi-stage charger”. First one acquired was CTEK 3300 (still have it, keep in car for emergency), then CTEK 4.3.

    With the latter I wall-mounted in garage adjacent to front/left corner of car (convenient to under-hood jump-start point and/or fuse box).

    When we bought in 2010, the car was seeing more typical daily use. But now my wife and I are both retired, our use of the car has ebbed, and I’ve gradually come ‘round to this:

    1. Tired of dealing with alligator clips, I installed the proprietary CTEK connector cable (typically their chargers come with this). The positive lead I connected where 12 volt feeds into fuse box, and neg lead you just need a convenient bolt location to hitchhike on.

    2. I follow this rule: if on any particular day the car is not going to see use, it gets connected to the charger, which runs it’s AGM cycle, then settles down to maintenance mode.

    3. The charger stays connected thus ‘til the car next sees use. Which typically can be a few days, upwards of a week, occasionally more.

    4. Periodically, the day after a drive and before connection to charger, I’ll check the battery’s health, using an electronic load tester. I’m using a somewhat venerable Clore Solar BA5. It requires connection right at the posts, so more often I’ll just assess voltage with a multimeter at the jump point.

    All of the above has worked out well with the current battery, installed September of 2015, still “apparently” doing well, but I appreciate it will expire sometime, so try to keep current with battery options, sources and prices. The latter just keep climbing.

    Prior to starting this charger regimen I’d be in constant turmoil, looking for excuses to run the car, which started to seem absurd.

    I appreciate this doesn’t work for everyone, just applicable for low use, garaged with 120 volt access.

    Again, our current battery was installed September of 2015, and for the most part of it's life I've followed the keep-it-on-a-charger regiment. Yesterday, after a two week downtime (on the charger the full time) I did a protracted drive, from North Coquitlam, almost to Deep Cove, through town to the international airport in Richmond, then back to North Coquitlam.

    When I got home I did @bisco's trick, popped the hood, (to avoid any electronic wake-up, from opening a door to pop the hood) And got an astounding 12.94 volt reading at the jump point. Then hooked up the charger.
     

    Attached Files:

    #8 Mendel Leisk, Dec 27, 2022
    Last edited: Dec 27, 2022
    rayluo likes this.
  9. rayluo

    rayluo Junior Member

    Joined:
    Jun 20, 2022
    13
    2
    0
    Location:
    Washington, USA
    Vehicle:
    2007 Prius
    Model:
    N/A
    I did not know CTEK 3300 or 4.3 before. It seems they are priced at sub $100, so, technically still at the same magnitude of the "inexpensive hobby chargers". The hobby charger I used can work with many different kind of batteries: Lithium Ion, Ni-MH (i.e. the one used by Prius traction battery), Lead Acid (typically 12v vehicle batteries), etc., thus more versatile. The CTEK seems to specialize on 12v vehicle batteries, thus presumably easier to operate.

    Why do you need to keep an on-grid charger in your car for emergency? If your 12v battery fails and you strand on the road where typically has no 110v grid power, what you would need is a starter battery, so that you can ignite the car immediately, and be able to make it to your home.

    Very impressive. Does your wife also get used to such a routine of "remember to unplug it before each drive (otherwise the charger on the wall - or the wall itself - would be torn down)", and you two never made any mistake? That is even more impressive.

    It is eye-opening to see how you meticulously maintain your 12v battery which worth only around $200. Now I wonder whether/how you maintain your traction battery which is typically listed at around $2000. :)
     
    #9 rayluo, Jan 26, 2023
    Last edited: Jan 26, 2023
  10. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    54,480
    38,106
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    I think as long as you do a longish drive every few weeks the traction battery get enough exercise. I hope.